North American porcine reproductive and respiratory syndrome (PRRS) virus and uses thereof

ABSTRACT

The invention provides isolated polynucleotide molecules that comprise a DNA sequence encoding an infectious RNA sequence encoding a genetically-modified North American PRRS virus, methods to make it and related polypeptides, polynucleotides, and various components. Vaccines comprising the genetically modified virus and polynucleotides and a diagnostic kit to distinguish between naturally infected and vaccinated animals are also provided.

The present application is a continuation of U.S. application Ser. No. 15/411,102, filed Jan. 20, 2017, which is a continuation of U.S. application Ser. No. 13/884,077, filed May 8, 2013, now U.S. Pat. No. 9,566,324, issued Feb. 14, 2017, and which represents the U.S. national stage (35 USC 371) of international application PCT/IB2011/055003, itself filed Nov. 9, 2011. The priority benefit under 35 USC 119(e) of U.S. provisional application 61/412,006, filed Nov. 10, 2010, is also claimed.

FIELD OF THE INVENTION

The present invention is in the field of animal health and is directed to infectious cDNA clones of positive polarity RNA viruses, novel RNA viruses and modified live forms thereof, and the construction of vaccines, in particular, swine vaccines, using such cDNA clones.

BACKGROUND OF THE INVENTION

Porcine reproductive and respiratory syndrome (PRRS) is characterized by abortions, stillbirths, and other reproductive problems in sows and gilts, as well as respiratory disease in young pigs. The causative agent is the PRRS virus (PRRSV), a member of the family Arteriviridae and the order Nidovirales. The nidoviruses are enveloped viruses having genomes consisting of a single strand of positive polarity RNA. The genomic RNA of a positive-stranded RNA virus fulfills the dual role in both storage and expression of genetic information. No DNA is involved in replication or transcription in Nidoviruses. The non-structural proteins are translated directly from the genomic RNA of nidoviruses as large polyproteins and subsequently cleaved by viral proteases into discreet functional proteins. A 3′-coterminal nested set of subgenomic RNAs (sgRNAs) is synthesized from the genome and are used as messenger RNAs for translation of the structural proteins. The reproduction of nidoviral genomic RNA is thus a combined process of genome replication and sgRNA synthesis.

In the late 1980's, two distinct genotypes of the virus emerged nearly simultaneously, one in North America and another in Europe. PRRS virus is now endemic in nearly all swine producing countries, and is considered one of the most economically important diseases affecting the global pork industry. Additionally, highly virulent genotypes have been isolated in China and surrounding countries, and such genotypes are generally related to North American genotypes.

Despite significant advances in understanding the biology of PRRSV, control of the virus remains difficult. Vaccination of animals in the field has proven to be largely ineffective. PRRS commonly re-emerges in immunized herds, and most on-farm PRRSV vaccination campaigns ultimately fail to control the disease.

Without being limited as to theory, infection of pigs with wild type PRRSV or their vaccination with a live attenuated form of this pathogen unfortunately only elicits an exuberant production of non-neutralizing antibodies. During this time interval, for example, only limited quantities of interferon (IFN)-γ (secreting cells are generated. Thus, PRRSV seems to inherently stimulate an imbalanced immune response distinguished by consistently abundant humoral (antibody-based) immunity, and a variable and limited but potentially protective T helper (Th) 1-like IFN-γ response. One characteristic of PRRSV infection that most likely contributes to the imbalanced development of adaptive immunity is the lack of an adequate innate immune response. Usually, virus-infected cells secrete type I interferon “IFN” (including IFN-α and IFN-β), which protects neighboring cells from infection. In addition, the released type I IFN interacts with a subset of naïve T cells to promote their conversion into virus-specific type II IFN (IFN-γ) secreting cells. In contrast, the IFN-α response of pigs to PRRSV exposure is nearly non-existent. Such inefficient stimulation of IFN-α production by a pathogen would be expected to have a significant impact on the nature of the host's adaptive immune response, since IFN-α up-regulates IFN-γ gene expression. Accordingly, the former cytokine controls the dominant pathway that promotes the development of adaptive immunity, namely, T cell-mediated IFN-γ responses and peak antiviral immune defenses.

In this regard, it has become evident that a probable link between innate and adaptive immunity in viral infections occurs through a special type of dendritic cell which has the ability to produce large amounts of type I interferon, and which plays a critical role in the polarization of T-cell function. Specifically, an infrequent but remarkable type of dendritic cell, the plasmacytoid dendritic cell (PDC), also known as a natural IFN-α/β-producing cell, plays a critical role in anti-viral immunity by means of their ability to cause naïve T cells to differentiate into IFN-γ secreting cells. Although rare, the PDC are enormously potent producers of IFN-α, with each cell being capable of producing 3-10 pg of IFN-α in response to virus. In contrast, monocytes produce 5- to 10-fold less IFN-α on a per cell basis. The phenotype and some biological properties of porcine PDC have been described (Summerfield et al., 2003, Immunology 110:440). Recent studies have determined that PRRSV does not stimulate porcine PDCs to secrete IFN-α (Calzada et al., 2010, Veterinary Immunology and Immunopathology 135:20).

This fact, in combination with the observation that exogenously added IFN-α at the time of vaccination has been found to improve the intensity of the PRRSV-specific IFN-γ response (W. A. Meier et al., Vet. Immunol. Immunopath. 102, pp 299-314, 2004), highlights the critical role that IFN-α plays during the infection of pigs with this virus. Given the apparent critical role of IFN-α on the development of protective immunity, it is important to determine the ability of different PRRS virus stocks to stimulate and/or inhibit the production of IFN-α. Accordingly, there is a pressing need for new and improved modified live vaccines to protect against PRRS. As described below, it is clear that viruses derived from the novel infectious cDNA clone, pCMV-S-P129-PK, and others, have a different phenotype than either the wild-type P129 virus or two commercially available modified live PRRS vaccines. Without being limited as to theory, the present invention provides for vaccines that facilitate cell-based immune response against the virus, and define a new and effective generation of PRRS vaccines.

SUMMARY OF THE INVENTION

In a first embodiment, the present invention provides an isolated polynucleotide molecule including a DNA sequence encoding an infectious RNA molecule encoding a PRRS virus that is genetically modified such that, as a vaccine, it elicits an effective immunoprotective response against the PRRS virus in porcine animals. In certain aspects, the invention provides for a DNA sequence as set forth herein including SEQ ID NO.:1, SEQ ID NO.:2, SEQ ID NO.:3, SEQ ID NO.:4, or SEQ ID: NO:6, or a sequence having at least 70% identity thereto, preferably 80% identity thereto, and more preferably 85%, 90%, 95%, 96%, 97%, 98% or 99% identity thereto.

In certain embodiments, the invention provides for a plasmid that includes an isolated polynucleotide molecule as set forth herein and a promoter capable of transcribing the polynucleotide molecule in a suitable host cell. In another embodiment, the North American or Chinese PRRS encoding sequence of the plasmid herein further encodes one or more detectable heterologous antigenic epitopes. The present invention provides for a transfected host cell that includes the plasmid set forth herein.

In another aspect, the present invention provides for a vaccine for protecting a porcine animal from infection by a PRRS virus. The vaccine may include a North American or Chinese PRRS virus encoded by an infectious RNA molecule, the infectious RNA molecule, or a plasmid, each of which are encoded by the isolated polynucleotide molecule as set forth herein. In yet another aspect, the vaccine includes a viral vector including the polynucleotide herein. The vaccine set forth herein may optionally include a vaccine carrier acceptable for veterinary use. In one important aspect, the vaccine has a decreased interferon-α inhibitory effect as compared to wild-type P129 PRRS virus (see ATCC 203488, 203489, U.S. Pat. No. 6,500,662).

In one embodiment, the present invention provides for diagnostic kit including polynucleotide molecules which distinguish (a so-called DIVA test) between porcine animals naturally infected with a field strain of a PRRS virus and porcine animals vaccinated with the modified live vaccine set forth herein.

In other embodiments, the invention provides for a method of protecting a porcine animal from infection with a strain of PRRS virus including administering to the animal an immunogenically protective amount of the vaccine of the claims set forth herein.

Further and preferred embodiments of the invention include an isolated Porcine Reproductive and Respiratory Syndrome Virus (PRRS), or a polynucleotide sequence encoding therefor, wherein the protein encoded by ORF1a is selected from a group consisting of those that contain any of the following amino acid sequences, wherein the underlined residues are believed to be novel: AMANVYD (SEQ ID NO: 9); IGHNAVM (SEQ ID NO: 12); TVPDGNC (SEQ ID NO: 15); CWWYLFD (SEQ ID NO: 18); HGVHGKY (SEQ ID NO: 21); AAKVDQY (SEQ ID NO: 24); PSATDTS (SEQ ID NO: 27); LNSLLSK (SEQ ID NO: 30); APMCQDE (SEQ ID NO: 33); CAPTGMD (SEQ ID NO: 36); PKVAKVS (SEQ ID NO: 39); AGEIVGV (SEQ ID NO: 42); ADFNPEK (SEQ ID NO: 45); and QTPILGR (SEQ ID NO: 48). In a further preferred embodiment of the invention, the invention provides an isolated North American or Chinese PRRS that contain any of the above-identified sequences within the protein encoded from ORF1a, including any combinations (2, 3, 4 . . . up to 17) of these identified sequences.

The invention further provides for an isolated Porcine Reproductive and Respiratory Syndrome Virus (PRRS) wherein the protein thereof encoded by ORF1a is selected from a group consisting of those amino acid sequences that contain any of: ANV (see SEQ ID NO: 9); HNA (see SEQ ID NO: 12); PDG (see SEQ ID NO: 15); WYL (see SEQ ID NO: 18); VHG (see SEQ ID NO: 21); KVD (see SEQ ID NO: 24); ATD (see SEQ ID NO: 27); SLL (see SEQ ID NO: 30); MCQ (see SEQ ID NO: 33); PTG (see SEQ ID NO: 36); VAK (see SEQ ID NO: 39); EIV (see SEQ ID NO: 42); FNP (see SEQ ID NO: 45); and PIL (see SEQ ID NO: 48), including any combinations (2, 3, 4 . . . up to 17) of these identified sequences.

In a further preferred embodiment, the invention provides an isolated North American or Chinese PRRS wherein, irrespective of the identity of any other specific nucleotide or amino acid sequence positions at any point in a polynucleotide encoding the virus or the proteins encoded therefrom, the ORF1a virus protein contains:

-   (a) any of the following specific amino acids in the specified     sequences, -   an amino acid N within the amino acid sequence ANV (see SEQ ID NO:     9); -   an amino acid N within the amino acid sequence HNA (see SEQ ID NO:     12); -   an amino acid D within the amino acid sequence PDG (see SEQ ID NO:     15); -   an amino acid Y within the amino acid sequence WYL (see SEQ ID NO:     18); -   an amino acid H within the amino acid sequence VHG (see SEQ ID NO:     21); -   an amino acid V within the amino acid sequence KVD (see SEQ ID NO:     24); -   an amino acid T within the amino acid sequence ATD (see SEQ ID NO:     27); -   an amino acid L within the amino acid sequence SLL (see SEQ ID NO:     30). -   an amino acid C within the amino acid sequence MCQ (see SEQ ID NO:     33); -   an amino acid T within the amino acid sequence PTG (see SEQ ID NO:     36); -   an amino acid A within the amino acid sequence VAK (see SEQ ID NO:     39); -   an amino acid I within the amino acid sequence EIV (see SEQ ID NO:     42); -   an amino acid N within the amino acid sequence FNP (see SEQ ID NO:     45); and -   amino acid I within the amino acid sequence PIL (see SEQ ID NO: 48),     to include any combinations (2, 3, 4 . . . up to 17) of these     identified sequences, or -   (b) contains said specific underlined single amino acids in the     specified 3-residue ORF1a peptide sequences of any other North     American or Chinese PRRS viruses that correspond to the 3-residue     sequences as specified above, taking into account that said other     specific 3-residue amino acid sequences may show one or two     additional amino sequence changes, but still be recognized as     corresponding to the sequences specified above. For the purposes of     this embodiment of the invention, “corresponding” means that the     relative sequences can be optimally aligned using a BLOSUM algorithm     as described in Henikoff et al. Proc Natl. Acad. Sci., USA, 89, pp.     10915-10919, 1992.

In a further preferred embodiment of the invention, an isolated Porcine Reproductive and Respiratory Syndrome Virus (PRRS) is provided wherein the protein thereof encoded by ORF1a has an amino acid sequence that contains one or more of variations (a), (b), (c) and (d), wherein each said variation is defined as follows:

-   variation (a), -   an amino acid N within the amino acid sequence ANV (see SEQ ID NO:     9); -   an amino acid N within the amino acid sequence HNA (see SEQ ID NO:     12); -   an amino acid D within the amino acid sequence PDG (see SEQ ID NO:     15), -   an amino acid Y within the amino acid sequence WYL (see SEQ ID NO:     18); -   an amino acid H within the amino acid sequence VHG (see SEQ ID NO:     21), or any subset of variation (a); -   variation (b), -   an amino acid V within the amino acid sequence KVD (see SEQ ID NO:     24); -   an amino acid T within the amino acid sequence ATD (see SEQ ID NO:     27); -   an amino acid L within the amino acid sequence SLL (see SEQ ID NO:     30). -   an amino acid C within the amino acid sequence MCQ (see SEQ ID NO:     33), or any subset of variation (b); -   variation (c), -   an amino acid T within the amino acid sequence PTG (see SEQ ID NO:     36); -   an amino acid A within the amino acid sequence VAK (see SEQ ID NO:     39), or any subset of variation (c); and -   variation (d), -   an amino acid I within the amino acid sequence EIV (see SEQ ID NO:     42); -   an amino acid N within the amino acid sequence FNP (see SEQ ID NO:     45); -   and amino acid I within the amino acid sequence PIL (see SEQ ID NO:     20), or any subset of variation (d) thereof.

Such PRRS viruses may further contain two or more of the five amino acid sequences identified in variation (a), and/or two or more of the four amino acid sequences identified in variation (b), and/or the two amino acid sequences identified in variation (c), and/or two or more of the three amino acid sequences identified in variation (d).

The present invention also provides a plasmid capable of directly transfecting a suitable host cell and expressing a Porcine Reproductive and Respiratory Syndrome Virus (PRRS) from the suitable host cell so transfected, which plasmid comprises: (a) a DNA sequence encoding an infectious RNA molecule encoding the PRRS virus, and (b) a promoter capable of transcribing said infectious RNA molecule, wherein the protein encoded by ORF1a of said virus has an amino acid sequence that contains:

-   (1) an amino acid N within the amino acid sequence ANV (see SEQ ID     NO: 9); -   an amino acid N within the amino acid sequence HNA (see SEQ ID NO:     12); -   an amino acid D within the amino acid sequence PDG (see SEQ ID NO:     15), -   an amino acid Y within the amino acid sequence WYL (see SEQ ID NO:     18); -   an amino acid H within the amino acid sequence VHG (see SEQ ID NO:     21), or any subset thereof; and/or -   (2) an amino acid V within the amino acid sequence KVD (see SEQ ID     NO: 24); -   an amino acid T within the amino acid sequence ATD (see SEQ ID NO:     27); -   an amino acid L within the amino acid sequence SLL (see SEQ ID NO:     30). -   an amino acid C within the amino acid sequence MCQ (see SEQ ID NO:     33), or any subset thereof; and/or -   (3) an amino acid T within the amino acid sequence PTG (see SEQ ID     NO: 36); -   an amino acid A within the amino acid sequence VAK (see SEQ ID NO:     39), or any subset thereof; and/or -   (4) an amino acid I within the amino acid sequence EIV (see SEQ ID     NO: 42); -   an amino acid N within the amino acid sequence FNP (see SEQ ID NO:     45); -   and amino acid I within the amino acid sequence PIL (see SEQ ID NO:     48), or any subset thereof.

It will be appreciated that ORF1a encodes a polyprotein comprising protease function, and ORF1b encodes a polyprotein comprising replicase (RNA polymerase) and helicase functions. Additional information concerning the functions for proteins encoded from various ORFs (open reading frames) of PRRS may be found, for example, in U.S. Pat. No. 7,132,106. See also U.S. Pat. No. 7,544,362 in regard of function of ORF7, and other open reading frames. As would be appreciated in the art, the ORF1-encoded proteins are expected to have additional functions, known and unknown, and the novel amino acid changes useful in the practice of the present invention are not limited via their effects on any one specific function of the ORF1-encoded proteins.

In further preferred embodiments, said plasmid contains a promoter that is a eukaryotic promoter capable of permitting a DNA launch in targeted eukaryotic cells, or a prokaryotic or phage promoter capable of directing in vitro transcription of the plasmid. The invention similarly provides a method of generating a PRRS virus, which method comprises transfecting a suitable host cell with an appropriate plasmid and obtaining PRRS virus generated by the transfected cell.

Accordingly, in a specific and preferred embodiment, the invention provides an isolated polynucleotide molecule comprising a DNA sequence encoding an infectious RNA molecule encoding a North American PRRS virus, wherein said DNA sequence is selected from the group consisting of:

-   (a) SEQ ID NO:6; -   (b) a sequence that has at least 85% identity to the DNA sequence     of (a) wherein the protein encoded by ORF1a thereof has an amino     acid sequence that contains: -   from group (b) (1) -   an amino acid N within the amino acid sequence ANV (see SEQ ID NO:     9); -   an amino acid N within the amino acid sequence HNA (see SEQ ID NO:     12); -   an amino acid D within the amino acid sequence PDG (see SEQ ID NO:     15), -   an amino acid Y within the amino acid sequence WYL (see SEQ ID NO:     18); -   an amino acid H within the amino acid sequence VHG (see SEQ ID NO:     21), or any subset thereof; and/or -   from group (b) (2) -   an amino acid V within the amino acid sequence KVD (see SEQ ID NO:     24); -   an amino acid T within the amino acid sequence ATD (see SEQ ID NO:     27); -   an amino acid L within the amino acid sequence SLL (see SEQ ID NO:     30). -   an amino acid C within the amino acid sequence MCQ (see SEQ ID NO:     33), or any subset thereof; and/or -   from group (b)(3) -   an amino acid T within the amino acid sequence PTG (see SEQ ID NO:     36); -   an amino acid A within the amino acid sequence VAK (see SEQ ID NO:     39), or any subset thereof; and/or -   from group (b)(4) -   an amino acid I within the amino acid sequence EIV (see SEQ ID NO:     42); -   an amino acid N within the amino acid sequence FNP (see SEQ ID NO:     45); -   and amino acid I within the amino acid sequence PIL (see SEQ ID NO:     20), or any subset thereof; and -   (c) a DNA sequence that hybridizes to the complement of a DNA     sequence of (a) or (b) under highly stringent conditions which     comprise hybridization to filter bound DNA in 0.5 M NaHPo4, 7% SDS,     1 mM EDTA at 65 degrees C., and washing in 0.1 SSC/0/1% SDS at 68     degrees C.

The invention also provides for host cells transfected with polynucleotide molecules and provides vaccines for protecting a porcine animal against infection by a PRRS virus, which vaccine comprises: (a) a genetically modified North American PRRS virus encoded by such aforementioned polynucleotide molecules, or (b) said infectious molecule, or (c) said polynucleotide molecule in the form of a plasmid, or (d) a viral vector comprising said polynucleotide molecule, wherein the PRRS virus is able to elicit an effective immunoprotective response against infection by PRRS virus, in an amount effective to produce immunoprotection against infection, and a carrier suitable for veterinary use.

The invention also provides RNA polynucleotide sequences corresponding to (i.e. by having complementary base coding sequences):

-   (a) the DNA sequence of SEQ ID NO:6; -   (b) a DNA sequence that has at least 85% identity to the DNA     sequence of (a) wherein the protein encoded by ORF1a thereof has an     amino acid sequence that contains any of the following, and any     combination of any of the following: -   an amino acid N within the amino acid sequence ANV (see SEQ ID NO:     9); -   an amino acid N within the amino acid sequence HNA (see SEQ ID NO:     12); -   an amino acid D within the amino acid sequence PDG (see SEQ ID NO:     15), -   an amino acid Y within the amino acid sequence WYL (see SEQ ID NO:     18); -   an amino acid H within the amino acid sequence VHG (see SEQ ID NO:     21), -   an amino acid V within the amino acid sequence KVD (see SEQ ID NO:     24); -   an amino acid T within the amino acid sequence ATD (see SEQ ID NO:     27); -   an amino acid L within the amino acid sequence SLL (see SEQ ID NO:     30). -   an amino acid C within the amino acid sequence MCQ (see SEQ ID NO:     33), -   an amino acid T within the amino acid sequence PTG (see SEQ ID NO:     36); -   an amino acid A within the amino acid sequence VAK (see SEQ ID NO:     39), -   (an amino acid I within the amino acid sequence EIV (see SEQ ID NO:     42); -   an amino acid N within the amino acid sequence FNP (see SEQ ID NO:     45); -   and amino acid I within the amino acid sequence PIL (see SEQ ID NO:     20), or -   (c) a DNA sequence that hybridizes to the complement of a DNA     sequence of (a) or (b) under highly stringent conditions which     comprise hybridization to filter bound DNA in 0.5 M NaHPo4, 7% SDS,     1 mM EDTA at 65 degrees C., and washing in 0.1 SSC/0/1% SDS at 68     degrees C.

Accordingly, the invention also provides diagnostic kits comprising polynucleotide molecules which distinguish between porcine animals naturally infected with a field strain of a PRRS virus and porcine animals vaccinated with the vaccines of the invention, which vaccines (viruses) preferably evidence a decreased interferon-α inhibitory effect as compared to wild-type P129 PRRS virus (SEQ ID NO:5).

BRIEF DESCRIPTION OF THE TABLES AND FIGURES

Table 1 shows infectious cDNA clones and the corresponding viruses that were derived by transfection into PK-9 cells.

Table 2 shows the interferon-α inhibitory effect of wild-type PRRS virus and derivatives adapted to growth in cell culture.

Table 3 delineates the interferon-α inhibitory effect of wild-type PRRS virus P129 and its genetically engineered derivatives adapted to grow in CD163-expressing PK-9 cells.

Table 4 shows decreased interferon-α inhibitory effect of the P129-PK-FL and P129-PK-d43/44 viruses as compared to the wild-type P129 virus and the PRRS Ingelvac vaccines.

Table 5 depicts the design of a study conducted to evaluate the safety and efficacy of vaccine viruses.

Table 6 shows all nucleotide differences and resulting amino acid differences between P129 passage 0 and P129-PK-FL passage 17, by genome position.

Table 7 shows a summary of nucleotide and amino acid differences between P129 passage 0 and P129-PK-FL passage 17, by viral protein.

Table 8 shows all nucleotide differences and resulting amino acid differences between the PRRSV genomes found in infectious cDNA clones pCMV-S-P129 and pCMV-S-P129-PK17-FL, by genome position.

Tables 9 and 10 show amino acid changes contributing to the phenotype of the Passage 52 virus (SEQ ID NO:6).

FIG. 1 shows rectal temperatures post-vaccination.

FIG. 2 shows rectal temperatures post-challenge with virulent PRRSV NADC20.

FIG. 3 shows body weights post-vaccination and post-challenge.

FIG. 4 shows post-challenge data for percentage of lungs with PRRS lesions.

FIG. 5 shows post-challenge lung assessment scores (LAS) for severity of lesions observed.

FIG. 6 is a histogram that depicts the anti-PRRSV antibody levels in serum post-vaccination and post-challenge (ELISA S/P ratios).

FIG. 7 is a graphical representation of post-challenge virus load in serum (log TCID50/ml on PAM cells)

FIG. 8 is a pictorial representation of the methods employed for obtaining the vaccines including SEQ ID NO:1 through SEQ ID NO:6, as disclosed herein.

BRIEF DESCRIPTION OF THE SEQUENCES

SEQ ID NO:1 provides the P129-PK-FL passage 17 complete genome.

SEQ ID NO:2 provides the P129-PK-d43/44 passage 17 complete genome.

SEQ ID NO:3 provides the P129-PK-FL passage 24 complete genome.

SEQ ID NO:4 provides the P129-PK-d43/44 passage 34 complete genome.

SEQ ID NO:5 provides the P129 passage 0 complete genome.

SEQ ID NO:6 provides the P129 passage 52 complete genome.

DETAILED DESCRIPTION OF THE INVENTION

As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. Thus, for example, references to “the method” includes one or more methods, and/or steps of the type described herein which will become apparent to those persons skilled in the art upon reading this disclosure and so forth.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the invention, the preferred methods and materials are now described.

The practice of the present invention will employ, unless indicated specifically to the contrary, conventional methods of virology, immunology, microbiology, molecular biology and recombinant DNA techniques within the skill of the art, many of which are described below for the purpose of illustration. Such techniques are explained fully in the literature. See, e.g., Sambrook, et al. Molecular Cloning: A Laboratory Manual (2nd Edition, 1989); Maniatis et al. Molecular Cloning: A Laboratory Manual (1982); DNA Cloning: A Practical Approach, vol. I & II (D. Glover, ed.); Oligonucleotide Synthesis (N. Gait, ed., 1984); Nucleic Acid Hybridization (B. Hames & S. Higgins, eds., 1985); Transcription and Translation (B. Hames & S. Higgins, eds., 1984); Animal Cell Culture (R. Freshney, ed., 1986); Perbal, A Practical Guide to Molecular Cloning (1984).

“North American PRRS virus” means any PRRS virus having genetic characteristics associated with a North American PRRS virus isolate, such as, but not limited to the PRRS virus that was first isolated in the United States around the early 1990's (see, e.g., Collins, J. E., et al., 1992, J. Vet. Diagn. Invest. 4:117-126); North American PRRS virus isolate MN-1b (Kwang, J. et al., 1994, J. Vet. Diagn. Invest. 6:293-296); the Quebec LAF-exp91 strain of PRRS (Mardassi, H. et al., 1995, Arch. Virol. 140:1405-1418); and North American PRRS virus isolate VR 2385 (Meng, X.-J et al., 1994, J. Gen. Virol. 75:1795-1801). Genetic characteristics refer to genomic nucleotide sequence similarity and amino acid sequence similarity shared by North American PRRS virus strains. Chinese PRRS virus strains generally evidence about 80-93% nucleotide sequence similarity with North American strains.

“European PRRS virus” refers to any strain of PRRS virus having the genetic characteristics associated with the PRRS virus that was first isolated in Europe around 1991 (see, e.g., Wensvoort, G., et al., 1991, Vet. Q. 13:121-130). “European PRRS virus” is also sometimes referred to in the art as “Lelystad virus”.

“An effective immunoprotective response”, “immunoprotection”, and like terms, for purposes of the present invention, mean an immune response that is directed against one or more antigenic epitopes of a pathogen so as to protect against infection by the pathogen in a vaccinated animal. For purposes of the present invention, protection against infection by a pathogen includes not only the absolute prevention of infection, but also any detectable reduction in the degree or rate of infection by a pathogen, or any detectable reduction in the severity of the disease or any symptom or condition resulting from infection by the pathogen in the vaccinated animal as compared to an unvaccinated infected animal. An effective immunoprotective response can be induced in animals that have not previously been infected with the pathogen and/or are not infected with the pathogen at the time of vaccination. An effective immunoprotective response can also be induced in an animal already infected with the pathogen at the time of vaccination.

A genetically modified PRRS virus is “attenuated” if it is less virulent than its unmodified parental strain. A strain is “less virulent” if it shows a statistically significant decrease in one or more parameters determining disease severity. Such parameters may include level of viremia, fever, severity of respiratory distress, severity of reproductive symptoms, or number or severity of lung lesions, etc.

“Host cell capable of supporting PRRS virus replication” means a cell which is capable of generating infectious PRRS when infected with a virus of the invention. Such cells include porcine cells of the monocyte/macrophage lineage such as porcine alveolar macrophage cells and derivatives, MA-104 monkey kidney cells and derivatives such as MARC-145 cells, and cells transfected with a receptor for the PRRS virus. The term “host cell capable of supporting PRRS virus replication” may also include cells within a live pig.

“Open reading frame”, or “ORF”, as used herein, means the minimal nucleotide sequence required to encode a particular PRRS virus protein without an intervening stop codon.

“Porcine” and “swine” are used interchangeably herein and refer to any animal that is a member of the family Suidae such as, for example, a pig. The term “PRRS virus”, as used herein, unless otherwise indicated, means any strain of either the North American or European PRRS viruses.

“PRRS” encompasses disease symptoms in swine caused by a PRRS virus infection. Examples of such symptoms include, but are not limited to, fever, abortion in pregnant females, respiratory distress, lung lesions, loss of appetite, and mortality in young pigs. As used herein, a PRRS virus that is “unable to produce PRRS” refers to a virus that can infect a pig, but which does not produce any disease symptoms normally associated with a PRRS infection in the pig.

PRRSV “N protein” or “ORF7” as used herein is defined as a polypeptide that is encoded by ORF7 of both the European and North American genotypes of PRRS virus. Examples of specific isotypes of N protein which are currently known are the 123 amino acid polypeptide of the North American PRRS prototype isolate VR2322 reported in Genbank by Accession numbers PRU87392, and the 128 residue N protein of European prototype PRRS isolate Lelystad reported in Genbank Accession number A26843.

“PRRSV N protein NLS-1 region” or “PRRSV ORF7 NLS-1 region” refers to a “pat4” or “nuc1” nuclear localization signal (Nakai & Kanehisa, 1992; Rowland & Yoo, 2003) containing four continuous basic amino acids (lysine or arginine), or three basic residues and a histidine or proline, located within about the first 15 N-terminal residues of the mature N protein. By way of example the VR2332 NLS-1 region sequence is KRKK and is located at residues 9-12, while the Lelystad isolate sequence is KKKK and is located at residues 10-13 of the N protein.

“PRRSV N protein NLS-2 region” or “PRRSV ORF7 NLS-2 region” refers to a second nuclear localization signal within the N protein that can take one of two forms. In North American PRRS viruses NLS-2 has a pattern which we have designated as the “pat8” motif, which begins with a proline followed within three residues by a five residue sequence containing at least three basic residues (K or R) out of five (a slight modification of the “pat7” or “nuc2” motif described by Nakai & Kanehisa, 1992; Rowland & Yoo, 2003). By way of example such a sequence is located at N protein residues 41-47 of the North American PRRSV isolate VR2332, and is represented by the sequence P . . . K In European PRRS viruses NLS-2 has a “pat4” or “nuc1” motif, which is a continuous stretch of four basic amino acids or three basic residues associated with histidine or proline (Nakai & Kanehisa, 1992; Rowland & Yoo, 2003). The NLS-2 of the European PRRSV isolate Lelystad is located at residues 47-50 and is represented by the sequence K . . . K

“PRRSV N protein NoLS region” or “PRRSV ORF7 NoLS region” refers to a nucleolar localization signal having a total length of about 32 amino acids and incorporating the NLS-2 region near its amino terminus. By way of example the VR2332 NoLS region sequence is located at residues 41-72 and is represented by the sequence P . . . R (Rowland & Yoo, 2003) and the corresponding Lelystad isolate sequence is located at residues 42-73 and is represented by the sequence P . . . R.

“Transfected host cell” means practically any host cell which as described in U.S. Pat. No. 5,600,662 when transfected with PRRS virus RNA can produce a at least a first round of PRRS virions.

An “infectious DNA molecule”, for purposes of the present invention, is a DNA molecule that encodes the necessary elements to support replication, transcription, and translation into a functional virion from a suitable host cell.

Likewise, an “isolated polynucleotide molecule” refers to a composition of matter comprising a polynucleotide molecule of the present invention purified to any detectable degree from its naturally occurring state, if any.

For purposes of the present invention, the nucleotide sequence of a second polynucleotide molecule (either RNA or DNA) is “homologous” to the nucleotide sequence of a first polynucleotide molecule, or has “identity” to said first polynucleotide molecule, where the nucleotide sequence of the second polynucleotide molecule encodes the same polyaminoacid as the nucleotide sequence of the first polynucleotide molecule as based on the degeneracy of the genetic code, or when it encodes a polyaminoacid that is sufficiently similar to the polyaminoacid encoded by the nucleotide sequence of the first polynucleotide molecule so as to be useful in practicing the present invention. Homologous polynucleotide sequences also refers to sense and anti-sense strands, and in all cases to the complement of any such strands. For purposes of the present invention, a polynucleotide molecule is useful in practicing the present invention, and is therefore homologous or has identity, where it can be used as a diagnostic probe to detect the presence of PRRS virus or viral polynucleotide in a fluid or tissue sample of an infected pig, e.g. by standard hybridization or amplification techniques. Generally, the nucleotide sequence of a second polynucleotide molecule is homologous to the nucleotide sequence of a first polynucleotide molecule if it has at least about 70% nucleotide sequence identity to the nucleotide sequence of the first polynucleotide molecule as based on the BLASTN algorithm (National Center for Biotechnology Information, otherwise known as NCBI, (Bethesda, Md., USA) of the United States National Institute of Health). In a specific example for calculations according to the practice of the present invention, reference is made to BLASTP 2.2.6 [Tatusova T A and T L Madden, “BLAST 2 sequences—a new tool for comparing protein and nucleotide sequences.” (1999) FEMS Microbiol Lett. 174:247-250.]. Briefly, two amino acid sequences are aligned to optimize the alignment scores using a gap opening penalty of 10, a gap extension penalty of 0.1, and the “blosum62” scoring matrix of Henikoff and Henikoff (Proc. Nat. Acad. Sci. USA 89:10915-10919. 1992). The percent identity is then calculated as: Total number of identical matches×100/divided by the length of the longer sequence+number of gaps introduced into the longer sequence to align the two sequences.

Preferably, a homologous nucleotide sequence has at least about 75% nucleotide sequence identity, even more preferably at least about 80%, 85%, 90% 95%, 96%, 97%, 98% and 99% nucleotide sequence identity. Since the genetic code is degenerate, a homologous nucleotide sequence can include any number of “silent” base changes, i.e. nucleotide substitutions that nonetheless encode the same amino acid.

A homologous nucleotide sequence can further contain non-silent mutations, i.e. base substitutions, deletions, or additions resulting in amino acid differences in the encoded polyaminoacid, so long as the sequence remains at least about 70% identical to the polyaminoacid encoded by the first nucleotide sequence or otherwise is useful for practicing the present invention. In this regard, certain conservative amino acid substitutions may be made which are generally recognized not to inactivate overall protein function: such as in regard of positively charged amino acids (and vice versa), lysine, arginine and histidine; in regard of negatively charged amino acids (and vice versa), aspartic acid and glutamic acid; and in regard of certain groups of neutrally charged amino acids (and in all cases, also vice versa), (1) alanine and serine, (2) asparagine, glutamine, and histidine, (3) cysteine and serine, (4) glycine and proline, (5) isoleucine, leucine and valine, (6) methionine, leucine and isoleucine, (7) phenylalanine, methionine, leucine, and tyrosine, (8) serine and threonine, (9) tryptophan and tyrosine, (10) and for example tyrosine, tyrptophan and phenylalanine. Amino acids can be classified according to physical properties and contribution to secondary and tertiary protein structure. A conservative substitution is recognized in the art as a substitution of one amino acid for another amino acid that has similar properties. Exemplary conservative substitutions may be found in WO 97/09433, page 10, published Mar. 13, 1997 (PCT/GB96/02197, filed Sep. 6, 1996. Alternatively, conservative amino acids can be grouped as described in Lehninger, (Biochemistry, Second Edition; Worth Publishers, Inc. NY:N.Y. (1975), pp. 71-77). Additional suitable conservative changes and the application thereof are described below.

Homologous nucleotide sequences can be determined by comparison of nucleotide sequences, for example by using BLASTN, above. Alternatively, homologous nucleotide sequences can be determined by hybridization under selected conditions. For example, the nucleotide sequence of a second polynucleotide molecule is homologous to SEQ ID NO:1 (or any other particular polynucleotide sequence) if it hybridizes to the complement of SEQ ID NO:1 under moderately stringent conditions, e.g., hybridization to filter-bound DNA in 0.5 M NaHPO₄, 7% sodium dodecyl sulfate (SDS), 1 mM EDTA at 65° C., and washing in 0.2×SSC/0.1% SDS at 42° C. (see Ausubel et al editors, Protocols in Molecular Biology, Wiley and Sons, 1994, pp. 6.0.3 to 6.4.10), or conditions which will otherwise result in hybridization of sequences that encode a PRRS virus as defined below. Modifications in hybridization conditions can be empirically determined or precisely calculated based on the length and percentage of guanosine/cytosine (GC) base pairing of the probe. The hybridization conditions can be calculated as described in Sambrook, et al., (Eds.), Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press: Cold Spring Harbor, N.Y. (1989), pp. 9.47 to 9.51.

In another embodiment, a second nucleotide sequence is homologous to SEQ ID NO:1 (or any other sequence of the invention) if it hybridizes to the complement of SEQ ID NO:1 under highly stringent conditions, e.g. hybridization to filter-bound DNA in 0.5 M NaHPO₄, 7% SDS, 1 mM EDTA at 65° C., and washing in 0.1×SSC/0.1% SDS at 68° C., as is known in the art (Ausebel et al. Current Protocols in Molecular Biology, Greene Publishing and Wiley Interscience, New York, 1989.

It is furthermore to be understood that the isolated polynucleotide molecules and the isolated RNA molecules of the present invention include both synthetic molecules and molecules obtained through recombinant techniques, such as by in vitro cloning and transcription.

Polynucleotide molecules can be genetically mutated using recombinant techniques known to those of ordinary skill in the art, including by site-directed mutagenesis, or by random mutagenesis such as by exposure to chemical mutagens or to radiation, as known in the art.” The mutations may be carried out by standard methods known in the art, e.g. site directed mutagenesis (see e.g. Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual, 2nd Ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.) of an infectious copy as described (e.g. Meulenberg et al., Adv. Exp. Med. Biol., 1998, 440:199-206).

Accordingly, the subject invention further provides a method for making a genetically modified North American PRRS virus, which method comprises mutating the DNA sequence encoding an infectious RNA molecule which encodes the PRRS virus as described above, and expressing the genetically modified PRRS virus using a suitable expression system. A genetically modified PRRS virus can be expressed from an isolated polynucleotide molecule using suitable expression systems generally known in the art, examples of which are described in this application. For example, the isolated polynucleotide molecule can be in the form of a plasmid capable of expressing the encoded virus in a suitable host cell in vitro, as is described in further detail below.

The North American PRRSV N protein sequences are highly conserved and the reported sequences have about 93-100% identity with each other. The North American and European PRRSV N proteins are about 57-59% identical and share common structural motifs. Generally, when comparing PRRS encoding sequences and isolates, which might be numbered differently as to specific nucleotides or encoded amino acids, identification of the proper regions are readily achieved by identifying preserved characteristic amino acids in a PRRS strain of interest and aligning it with a reference strain.

Recombinant DNA technology comprises extremely varied and powerful molecular biology techniques aimed at modifying nucleic acids at the DNA level and makes it possible to analyze and modify genomes at the molecular level. In this respect, viruses such as the PRRS virus because of the modest size of its genome is particularly amenable to such manipulations. However, recombinant DNA technology is not immediately applicable to non-retroviral RNA viruses because these viruses do not encompass a DNA intermediate step in their replication. For such viruses, infectious cDNA clones have to be developed before recombinant DNA technology can be applied to their genome to generate modified virus. Infectious clones can be derived through the construction of full-length (genomic length) cDNA (here used in the broad sense of a DNA copy of RNA and not only in the strict sense of a DNA copy of mRNA) of the virus under study, after which an infectious transcript is synthesized in vivo in cells transfected with the full-length cDNA, but infectious transcripts can also be obtained by in vitro transcription from full-length cDNA in a plasmid having a prokaryotic promoter in the presence of a transcription cocktail, or again in vitro using ligated partial-length cDNA fragments that comprise the full viral genome. In all cases, the transcribed RNA carries all the modifications that have been introduced to the cDNA and can be used to further passage the thus modified virus.

The preparation of an infectious clone of a European PRRS virus isolate or Lelystad virus is described in U.S. Pat. No. 6,268,199 which is hereby fully incorporated by reference. The preparation of an infectious cDNA clone of a North American PRRS virus isolate designated P129 (Lee et al., 2005; Yoo et al., 2004) is described in U.S. Pat. No. 6,500,662 which is hereby incorporated fully by reference. The sequence of P129 cDNA is disclosed in Genbank Accession Number AF494042 and in U.S. Pat. No. 6,500,662. Our work below makes use of such an infectious clone which in the context of a plasmid is expressed by the CMV immediate early promoter and has been designated pCMV-S-P129 and is also disclosed within U.S. Pat. No. 6,500,662. As described in U.S. Pat. No. 6,500,662 there are other plasmids and promoters suitable for use here.

Given the complete sequence of any open reading frame of interest and the location of an amino acid residue of interest, one of ordinary skill need merely consult a codon table to design changes at the particular position desired.

Codons constitute triplet sequences of nucleotides in mRNA and their corresponding cDNA molecules. Codons are characterized by the base uracil (U) when present in a mRNA molecule but are characterized by base thymidine (T) when present in DNA. A simple change in a codon for the same amino acid residue within a polynucleotide will not change the sequence or structure of the encoded polypeptide. It is apparent that when a phrase stating that a particular 3 nucleotide sequence “encode(s)” any particular amino acid, the ordinarily skilled artisan would recognize that the table above provides a means of identifying the particular nucleotides at issue. By way of example, if a particular three nucleotide sequence encodes lysine, the table above discloses that the two possible triplet sequences are AAA and AAG. Glycine is encoded by GGA, GGC, GGT (GGU if in RNA) and GGG. To change a lysine to glycine residue in an encoded protein one might replace a AAA or AAG triplet with any of by GGA and GGC, GGT or GGG in the encoding nucleic acid.

As aforementioned, the present invention is directed to the provision of vaccine strains of PRRS wherein host responses to the virus that are mediated by interferon pathways, among other responses, are not downregulated. As described in detail below, there are various modifications to the viral genome that are effective in this regard, particularly those found in ORF1a as disclosed herein, and combinations thereof. It should be noted that similar modification points can be found in additional open reading frames of the PRRS genome, as also disclosed herein (see Table 9).

It is noteworthy that certain other prior approaches to modification of the PRRS polynucleotide have been successful in order to attenuate the PRRS virus, possibly providing suitability for vaccine use, although the exact cause of the resultant attenuations is not generally known. For example, it has been disclosed to attenuate a virulent PRRS virus by mutating or deleting the NLS-2 region, NoLS region, or the NES region in the nucleocapsid or N protein (encoded by ORF7) of the virus, to include a deletion in open reading frame 7 (ORF7). In another aspect the ORF7 deletion is within the sequence encoding a nuclear localization signal (NLS) of a capsid protein. The ORF7 deletion within the sequence encoding an NLS may include deletion of one or more amino acids at positions 43-48 or deletion of an amino acid at either or both positions 43 and 44. See, for example, the entire disclosure of U.S. Pat. No. 7,544,362 which is incorporated by reference. The nucleocapsid protein (N) of PRRSV, which is encoded by ORF7, is a small basic protein that is phosphorylated (Wootton, Rowland, and Yoo, 2002) and forms homodimers (Wootton and Yoo, 2003). The crystal structure has recently been determined (Doan and Dokland, 2003). The N protein appears to have multiple functions in the infected cell. In addition to forming a spherical capsid structure into which genomic RNA is packaged, a process that takes place in the cytoplasm, a portion of N protein is transported into the nucleus and specifically to the nucleolus of the infected cell. The amino acid sequence of N protein contains two nuclear localization signals (NLS), a nucleolar localization signal (NoLS), and a nuclear export signal (NES) that facilitate transport into the nucleus and nucleolus, and export from the nucleus, respectively (Rowland et al., 1999; Rowland et al., 2003; Rowland and Yoo, 2003). While in the nucleolus, the N protein interacts with the small nucleolar RNA-associated protein fibrillarin and may regulate rRNA processing and ribosome biogenesis in the infected cell in order to favor virus replication (Yoo et al., 2003). Viral mutations of this type are valuable, either alone or in combination with other attenuating mutations, for designing novel PRRS vaccines. In another example of a PRRS virus that has been attenuated, modified to ORF1a was employed. Deletion of the DNA sequence encoding the antigenic epitope between amino acids 616 to 752 in the hypervariable region in the nonstructural protein 2 coding region of ORF1a was employed, see. U.S. Pat. No. 7,618,797, which is incorporated by reference in its entirety.

Studies on the immunobiology of PRRS virus are suggestive that the interaction of PRRS virus with PDCs merits examination. This cell type represents 0.2%-0.8% of peripheral blood mononuclear cells in humans, mice, rats, pigs and monkeys. Despite its scarcity, this cell is an important component of the innate immune system and is capable of secreting copious amounts of IFN-α following viral stimulation. It is through the secretion of IFN-α that PDCs play a major role in regulating antiviral innate and adaptive immunity since they promote the function of natural killer cells, B cells, and T cells. Furthermore, the maturation of porcine monocyte derived dendritic cells (MoDC) is aided by the IFN-α secreted by PDCs resulting in an enhanced ability of MoDCs to present antigen and activate T cells. At a later stage of viral infection, PDCs differentiate into a unique type of mature dendritic cell, which directly regulates the function of T cells and direct the differentiation of T cells into cells capable of secreting IFN-γ, which is a major mediator of antiviral immunity against viruses including PRRS virus. Not surprisingly there are human viruses, such as respiratory syncitial virus and measles virus, which are known to suppress the ability of PDCs to secrete IFN-α. This inhibitory effect is thought to play a role in the predominance of a humoral immune response and the associated immunopathology observed as a result of the infection with these viruses, as well as in the increased susceptibility of the host to secondary bacterial and viral infections.

In contrast, the wild-type PRRSV isolates as well as both of the Ingelvac PRRS vaccine strains (see Examples 5 and following, below) inhibited the ability of purified populations of porcine PDC to produce IFN-α, while the novel P129-PK-FL and P129-PK-d43/44 virus stocks (see below) exhibited a minimal to nil inhibitory effect on this PDC function. The significance of these observations resides, in part, on the importance of IFN-α in regulating the development of the adaptive immune response to viruses. Accordingly, it is very likely that an attenuated virus vaccine derived from a minimally IFN-α suppressing virus would elicit a strong antiviral protective immune response. It has previously been demonstrated the adjuvant effect of IFN-α on the Ingelvac PRRS MLV vaccine induced virus-specific T cell mediated IFN-γ response, and that the intensity of the virus-specific T cell mediated IFN-γ response elicited by the vaccine has a positive correlation with protective immunity against the virus under field and laboratory conditions. Accordingly, although not being limited as to theory, it would be reasonable to expect that the cell-mediated immune response and level of protective immunity elicited by a non-IFN-α-inhibitory PRRSV will be significantly greater than that of a PRRSV isolate exhibiting the wild-type (IFN-α inhibitory) phenotype.

Referring to the present invention, it is notable that the P129-PK-FL virus as well as all five deletion mutants derived from the pCMV-S-P129-PK infectious cDNA clone lost the ability to inhibit IFN-α production. Therefore this unusual phenotype can not be solely due to the deletions, but must be due at least in part to genetic changes that became fixed during construction of the infectious clone. Interestingly, uncloned P129 virus that was serially passaged 63 times on PK-9 cells retained the ability to inhibit IFN induction (Table 1). The most likely explanation for the common IFN phenotype seen in all infectious clone-derived viruses is the incorporation of one or more mutations during the generation of the infectious clone. These mutations would have existed, possibly at low levels, in the viral RNA used to construct the infectious clone. Ultimately, the mutations may have existed in the original (passage 0) virus in the pig or they may have been generated and enriched during the process of adapting the virus to growth on PK-9 cells for 16 passages. The possibility that the mutations were the result PCR-induced errors or cloning artifacts cannot be ruled out. At any rate, the mutation(s) responsible for the loss of the IFN-α inhibitory function became “fixed” during infectious clone construction, and would be expected to be present in all viruses derived from this particular infectious clone.

The possibility that mutations responsible for the altered IFN-α inhibition phenotype pre-existed in the viral RNA used to construct the cDNA clone is likely, given that PRRSV is known to readily generate random genetic diversity as a result of errors by the viral RNA-dependent RNA polymerase. Virus quasi-species are comprised of a heterogeneous mixture of closely related genetic variants that naturally appear during virus replication in vivo. Even more relevant is the observation of virus quasi-species after multiple in vitro passages of PRRSV derived from an infectious cDNA clone. This is notable since the starting population of virus genomes in previously conducted studies consisted of a genetically homogenous population, and sequence diversity was rapidly generated during passage in cell culture. In the current study, the level of genomic heterogeneity would have been higher, since the original P129 virus had not been cloned (biologically or molecularly) prior to the 16 PK-9 passages leading up to construction of the infectious clone. Thus the chance selection of a PRRSV RNA variant responsible for the loss of IFN-α inhibition function from among the quasi-species, and incorporation into the pCMV-S-P129-PK17-FL infectious cDNA clone seems plausible. The incorporation of these mutations into an infectious clone might be considered fortuitous, under some circumstances, given that all derivative viruses should share this distinct biological phenotype which may prove important for the development of effective next-generation PRRS vaccines.

The wild-type PRRS virus strain P129, like other strains of this virus, exhibited a strong inhibitory effect on the ability of peripheral blood mononuclear cells (PBMCs) and plasmacytoid dendritic cells (PDCs) to produce interferon (IFN)-α. On the other hand, virus derived from an infectious cDNA clone of P129 (pCMV-S-P129-PK17-FL) exhibited a significant reduction in the IFN-α inhibitory phenotype. This infectious clone was constructed from virus which was previously adapted to grow on the CD163-expressing porcine kidney cell line PK-9 over the course of 16 serial passages (see U.S. Pat. No. 7,754,464 which is incorporated by reference in its entirety). The IFN-α inhibitory phenotype of P129-PK-FL and P129-PK-d43/44 ranged from low to negligible and was in marked contrast to that exhibited by either of the two Ingelvac PRRS modified live virus vaccine strains, both of which were highly inhibitory. These results indicate that the P129-PK-FL and P129-PK-d43/44 viruses are biologically distinct from the parental low-passage P129 isolate, other wild-type PRRS viruses, and both Ingelvac PRRS vaccines. The potential implications of the reduced IFN-α-inhibitory phenotype, as well as possible reasons for the phenotypic change, are discussed.

Amino Acid Modifications of the Invention

According to the practice of the present invention, novel isolates of PRRS, whether of North American or Chinese genotypes, may be field-identified that contain specific contain amino acids at specific positions in the proteins encoded from ORF1, and which confer desirable phenotypes on these viruses. In the alternative, as aforementioned, standard genetic procedures may be employed to modify the genetic sequence (and thus the amino acid sequence) of the encoded ORF1 protein, again to produce modified North American and Chinese PRRS viruses, and infectious clones, and vaccines therefrom, all which provide such phenotypes. In preferred examples the phenotypes include, without limitation, decreased interferon-α inhibitory effect as compared to wild-type PRRS virus, and, optionally, the ability to reproduce or persist in a host animal (a pig) while triggering a robust immune response, but with little detectable pathology.

Thus, in the practice of the invention, North American PRRS strains or isolates that may serve as useful starting points include those disclosed, for example in U.S. Pat. Nos. 6,500,662; 7,618,797; 7,691,389, 7,132,106; 6,773, 908; 7,264,957; 5,695,766; 5,476,778; 5,846,805; 6,042,830; 6,982,160; 6,241,990; and 6,110,468. In regard of Chinese PRRS strains and isolates that may serve as useful starting points, see for example, published Chinese application CN200910091233.6 from Chinese application CN201633909 pertaining to the TJM-92 virus.

In connection with the discussion that follows, internationally recognized single and three-letter designations are used for the most common amino acids encoded by DNA: alanine (Ala, A); arginine (Arg, R); asparagine (Asn, N); aspartic acid (Asp, D); cysteine (Cys, C); glutamic acid (Glu, E); glutamine (Gln, Q); glycine (Gly, G); histidine (His, H); isoleucine (Ile, I); leucine (Leu, L); lysine (Lys, K); methionine (Met, M); phenylalanine (Phe, F); proline (Pro, P); serine (ser, S); threonine (Thr, T); tryptophan (Trp, W); tyrosine (Tyr, Y) and Valine (Val, V).

Tables 9 and 10 identify observed amino acid changes responsible for attenuation of virulence in North American (and Chinese) PRRS which correlate with reduced inhibition of interferon alpha activity, thereby permitting a safe and robust immune response to vaccines. Table 10 identifies highly preferred amino acid modifications in this regard, within ORF1a, and shows how these mutations have arisen in regard of passaging from other P129 cultures (it should be noted that the inspection of this history also facilitates design of mutagenesis strategies to (re) construct encoding DNA having any of the amino acid changes of the invention, as needed). In this regard, the most preferred amino acid improvements to ORF1a (as evidenced by P129 passage 52 include: asparagine at 182, asparagine at 189, tyrosine at 273, histidine at 302, threonine at 665, cysteine at 943, threonine at 1429, alanine at 1505, asparagine at 2410, which also potentially adds numerous glycoslation opportunities and which may further alter protein function.

Accordingly, the invention provides an isolated Porcine Reproductive and Respiratory Syndrome Virus (PRRS) wherein the protein thereof encoded by ORF1a is selected from a group consisting of those amino acid sequences that contain any of:

-   an amino acid N within the amino acid sequence AMANVYD (SEQ ID NO:     9); -   an amino acid N within the amino acid sequence IGHNAVM (SEQ ID NO:     12); -   an amino acid D within the amino acid sequence TVPDGNC (SEQ ID NO:     15); -   an amino acid Y within the amino acid sequence CWWYLFD (SEQ ID NO:     18); -   an amino acid H within the amino acid sequence HGVHGKY (SEQ ID NO:     21); -   an amino acid V within the amino acid sequence AAKVDQY (SEQ ID NO:     24); -   an amino acid T within the amino acid sequence PSATDTS (SEQ ID NO:     27); -   an amino acid L within the amino acid sequence LNSLLSK (SEQ ID NO:     30). -   an amino acid C within the amino acid sequence APMCQDE (SEQ ID NO:     33); -   an amino acid T within the amino acid sequence CAPTGMD (SEQ ID NO:     36); -   an amino acid A within the amino acid sequence PKVAKVS (SEQ ID NO:     39); -   an amino acid I within the amino acid sequence AGEIVGV (SEQ ID NO:     42); -   an amino acid N within the amino acid sequence ADFNPEK (SEQ ID NO:     45); and -   an amino acid I within the amino acid sequence QTPILGR (SEQ ID NO:     48).

More specifically, the invention provides an isolated Porcine Reproductive and Respiratory Syndrome Virus (PRRS) wherein the protein thereof encoded by ORF1a is selected from a group consisting of those amino acid sequences that contain any of:

-   an amino acid N within the amino acid sequence ANV (see SEQ ID NO:     9); -   an amino acid N within the amino acid sequence HNA (see SEQ ID NO:     12); -   an amino acid D within the amino acid sequence PDG (see SEQ ID NO:     15); -   an amino acid Y within the amino acid sequence WYL (see SEQ ID NO:     18); -   an amino acid H within the amino acid sequence VHG (see SEQ ID NO:     21); -   an amino acid V within the amino acid sequence KVD (see SEQ ID NO:     24); -   an amino acid T within the amino acid sequence ATD (see SEQ ID NO:     27); -   an amino acid L within the amino acid sequence SLL (see SEQ ID NO:     30). -   an amino acid C within the amino acid sequence MCQ (see SEQ ID NO:     33); -   an amino acid T within the amino acid sequence PTG (see SEQ ID NO:     36); -   an amino acid A within the amino acid sequence VAK (see SEQ ID NO:     39); -   an amino acid I within the amino acid sequence EIV (see SEQ ID NO:     42); -   an amino acid N within the amino acid sequence FNP (see SEQ ID NO:     45); and -   amino acid I within the amino acid sequence PIL (see SEQ ID NO: 48).

As aforementioned, there are numerous known strains and isolates of North American and Chinese PRRS, and novel strains continue to evolve or to be isolated. Although a high level of amino acid sequence homology exists between all these strains, those skilled in the art will immediately recognize that some variation does exist, and indeed advantage can be taken of these differences and similarities to further improve the phenotypic properties of all vaccine strains.

First, in regard of all of the amino acid motifs defined by SEQ ID NOS as specified directly (on Pages 27-28) above, the underlined and preferred amino acids (as provided from P129 passage 52) generally remain fully beneficial even if adjacent amino acids have otherwise changed from the specified SEQ ID NO sequences. Thus in regard of AMANVYD (SEQ ID NO: 9), as a specific and representative example, it is generally possible to inspect the corresponding ORF1-expressed protein sequence from any North American or Chinese PRRS, to find the corresponding amino acid motif, even if additional changes have occurred in such other strains, as a result of evolution, causing substitutions and/or deletions or additions. As will be appreciated by those skilled in the art, the preferred amino acid changes evidenced by P129 passage 52 should thus also remain operable in spite of other changes in overall amino acid sequence that are directly 5′ or 3′ to the specified amino acid of Passage 52. This will be so especially if the comparative amino acid changes are considered conservative. Thus in regard of AMANVYD (SEQ ID NO: 9), and the subsequence ANV thereof, it should be readily possible to identify the comparable motif in another PRRS strain if, for example, the valine therein is replaced by isoleucine or leucine, or any other residue, or if a residue is simply missing or an additional residue added. Numerous computer programs exist to identify alignments and thus determine if polypeptide sequence motifs correspond, for example the so-called Blosum tables (based on a given level of percent identity), see S. Henikoff et al. “Amino Acid Substitution matrices from protein blocks”, Proc Natl Acad Sci, USA, 89(22), pp. 10915-10919, Nov. 15, 1992, and see also A. L. Lehninger et al. Principles of Biochemistry, 2005, MacMillan and Company, 4^(th) edition. Conservative amino acid changes are also recognized based on categorization into 5 overall groups: sulfydryl (Cys); aromatic (Phe, Tyr, and Trp); basic (Lys, Arg, His); aliphatic (Val, Ileu, Leu, Met), and hydrophilic (Ala, Pro, Gly, Glu, Asp, Gln, Asn, Ser and Thr). Thus it is within the practice of the invention to modify any North American or Chinese PRRS encoding nucleotide sequence to incorporate at the appropriate and corresponding position, any of the amino acid changes specified for P129 passage 52, even if one or more of the other amino acids adjacent to the designated position have been added, deleted or substituted.

Additionally, based on similar principles, those skilled in the art will recognize that once a preferred amino acid is identified from the specific Passage 52 changes identified for ORF1a according to the practice of the present invention, that conservative replacements for any such passage 52 amino acids can then also be used, either in P129 variants, or in regard of any other North American or Chinese strains, with substantial preservation of the intended passage 52 phenotype. Thus, as representative examples: in regard of SLL (within SEQ ID NO: 30), the designated leucine residue may be further replaced with isoleucine, valine or methionine; in regard of FNP (within SEQ ID NO: 45), the designated asparagine may be replaced with any of Ala, Pro, Gly, Glu, Asp, Gln, Ser and Thr; and in regard of VAK (see SEQ ID NO: 39), the designated alanine may be replaced with any of Asn, Pro, Gly, Glu, Asp, Gln, Ser and Thr; all and the like, although it will be readily recognized that it is not a requirement of the present invention that any such replacement amino acids work as well as originally identified unique Passage 52 amino acid changes, at the specified locations. Of course, use of standard conservative amino acid changes according to any other recognized model also is practiced in the present invention. For example, and including vice-versa in all cases, Asp for Glu and vice versa, Asn for Gln, Arg for Lys, Ser for Cys or Thr, Phe for Tyr, Val for Leu or Ileu, Ala for Gly, and the like.

Further, within the practice of the present invention, although any of the individual Passage 52 amino acid changes (as identified for ORF1a above) can be usefully placed in any North American of Chinese PRRS with desired phenotypic effect, it is further preferred to in include as many of the Table 9 or Table 10 amino acid selections as possible in a final construct, as typically provided for by appropriate modification of the encoding polynucleotide sequence. Thus, the practice of the present invention includes the provision of Chinese or North American PRRS viruses (and corresponding encoding polynucleotides) that provide for 2, 3, 4, 5, 6, 7, 8, 9, and up to any of the approximately 17 identified Passage 52 ORF1a changes, (Table 9) all within a final viral sequence, to include any specific pairs, triplets, or other higher combinations of all the total identified Passage 52 amino acid changes. Such amino acid changes may, of course, be introduced into the corresponding encoding nucleotide sequences of the virus by site directed mutagenesis, PCR, and other techniques as are well known in the art.

To demonstrate that a particular genetically modified strain is attenuated an experiment described as follows may be used.

At least 10 gilts per group are included in each trial, which are derived from a PRRSV-free farm. Animals are tested free of PRRS virus specific serum antibodies and negative for PRRSV. All animals included in the trial are of the same source and breed. The allocation of the animals to the groups is randomized.

Challenge is performed at day 90 of pregnancy with intranasal application of 1 ml PRRSV with 10⁵ TCI D₅₀ per nostril. There are at least three groups for each test setup: One group for P129 challenge; one test group for challenge with the possibly attenuated virus; and one strict control group.

The study is deemed valid when the strict controls stay PRRSV-negative over the time course of the study and at least 25% less live healthy piglets are born in the P129 challenged group compared to the strict controls.

Attenuation, in other words less virulence, is defined as the statistical significant change of one or more parameters determining reproductive performance or other symptomology:

Significant reduction in at least one of the following parameters for the test group (possibly attenuated virus) compared to the unmodified parental strain infected group would be an indication of attenuation:

-   a) frequency of stillborns -   b) abortion at or before day 112 of pregnancy -   c) number of mummified piglets -   d) number of less lively and weak piglets -   e) pre-weaning mortality     Furthermore a significant increase in one of the following     parameters for the test group compared the unmodified parental     strain infected group is preferred: -   f) number of piglets weaned per sow -   g) number of live healthy piglets born per sow     In the alternative, respiratory symptoms and other symptoms of PRRSV     infection could be examined to establish attenuation.

An attenuated strain is valuable for the formulation of vaccines. The present vaccine is effective if it protects a pig against infection by a PRRS virus. A vaccine protects a pig against infection by a PRRS virus if, after administration of the vaccine to one or more unaffected pigs, a subsequent challenge with a biologically pure virus isolate (e.g., VR 2385, VR 2386, P129 etc.) results in a lessened severity of any gross or histopathological changes (e.g., lesions in the lung) and/or of symptoms of the disease, as compared to those changes or symptoms typically caused by the isolate in similar pigs which are unprotected (i.e., relative to an appropriate control). More particularly, the present vaccine may be shown to be effective by administering the vaccine to one or more suitable pigs in need thereof, then after an appropriate length of time (e.g., 4 weeks), challenging with a large sample (10⁽³⁻⁷⁾TCID₍₅₀₎) of a biologically pure PRRSV isolate. A blood sample is then drawn from the challenged pig after about one week, and an attempt to isolate the virus from the blood sample is then performed. Isolation of a large amount of the virus is an indication that the vaccine may not be effective, while isolation of reduced amounts of the virus (or no virus) is an indication that the vaccine may be effective.

Thus, the effectiveness of the present vaccine may be evaluated quantitatively (i.e., a decrease in the percentage of consolidated lung tissue as compared to an appropriate control group) or qualitatively (e.g., isolation of PRRSV from blood, detection of PRRSV antigen in a lung, tonsil or lymph node tissue sample by an immunoassay). The symptoms of the porcine reproductive and respiratory disease may be evaluated quantitatively (e.g., temperature/fever) or semi-quantitatively (e.g., the presence or absence of one or more symptoms or a reduction in severity of one or more symptoms, such as cyanosis, pneumonia, lung lesions etc.).

An unaffected pig is a pig which has either not been exposed to a porcine reproductive and respiratory disease infectious agent, or which has been exposed to a porcine reproductive and respiratory disease infectious agent but is not showing symptoms of the disease. An affected pig is one which shows symptoms of PRRS or from which PRRSV can be isolated.

Vaccines of the present invention can be formulated following accepted convention to include acceptable carriers for animals, including humans (if applicable), such as standard buffers, stabilizers, diluents, preservatives, and/or solubilizers, and can also be formulated to facilitate sustained release. Diluents include water, saline, dextrose, ethanol, glycerol, and the like. Additives for isotonicity include sodium chloride, dextrose, mannitol, sorbitol, and lactose, among others. Stabilizers include albumin, among others. Other suitable vaccine vehicles and additives, including those that are particularly useful in formulating modified live vaccines, are known or will be apparent to those skilled in the art. See, e.g., Remington's Pharmaceutical Science, 18th ed., 1990, Mack Publishing, which is incorporated herein by reference.

Vaccines of the present invention can further comprise one or more additional immunomodulatory components such as, e.g., an adjuvant or cytokine, among others. Non-limiting examples of adjuvants that can be used in the vaccine of the present invention include the RIBI adjuvant system (Ribi Inc., Hamilton, Mont.), alum, mineral gels such as aluminum hydroxide gel, oil-in-water emulsions, water-in-oil emulsions such as, e.g., Freund's complete and incomplete adjuvants, Block copolymer (CytRx, Atlanta, Ga.), QS-21 (Cambridge Biotech Inc., Cambridge Mass.), SAF-M (Chiron, Emeryville Calif.), AMPHIGEN® adjuvant, saponin, Quil A or other saponin fraction, monophosphoryl lipid A, and Avridine lipid-amine adjuvant. Non-limiting examples of oil-in-water emulsions useful in the vaccine of the invention include modified SEAM62 and SEAM 1/2 formulations. Modified SEAM62 is an oil-in-water emulsion containing 5% (v/v) squalene (Sigma), 1% (v/v) SPAN.®. 85 detergent (ICI Surfactants), 0.7% (v/v) TWEEN® 80 detergent (ICI Surfactants), 2.5% (v/v) ethanol, 200 pg/ml Quil A, 100 [mgr]g/ml cholesterol, and 0.5% (v/v) lecithin. Modified SEAM 1/2 is an oil-in-water emulsion comprising 5% (v/v) squalene, 1% (v/v) SPAN.®. 85 detergent, 0.7% (v/v) Tween 80 detergent, 2.5% (v/v) ethanol, 100 .mu.g/ml Quil A, and 50 .mu.g/ml cholesterol. Other immunomodulatory agents that can be included in the vaccine include, e.g., one or more interleukins, interferons, or other known cytokines.

Vaccines of the present invention can optionally be formulated for sustained release of the virus, infectious RNA molecule, plasmid, or viral vector of the present invention. Examples of such sustained release formulations include virus, infectious RNA molecule, plasmid, or viral vector in combination with composites of biocompatible polymers, such as, e.g., poly(lactic acid), poly(lactic-co-glycolic acid), methylcellulose, hyaluronic acid, collagen and the like. The structure, selection and use of degradable polymers in drug delivery vehicles have been reviewed in several publications, including A. Domb et al., 1992, Polymers for Advanced Technologies 3: 279-292, which is incorporated herein by reference. Additional guidance in selecting and using polymers in pharmaceutical formulations can be found in texts known in the art, for example M. Chasin and R. Langer (eds), 1990, “Biodegradable Polymers as Drug Delivery Systems” in: Drugs and the Pharmaceutical Sciences, Vol. 45, M. Dekker, N.Y., which is also incorporated herein by reference. Alternatively, or additionally, the virus, plasmid, or viral vector can be microencapsulated to improve administration and efficacy. Methods for microencapsulating antigens are well-known in the art, and include techniques described, e.g., in U.S. Pat. Nos. 3,137,631; 3,959,457; 4,205,060; 4,606,940; 4,744,933; 5,132,117; and International Patent Publication WO 95/28227, all of which are incorporated herein by reference.

Liposomes can also be used to provide for the sustained release of virus, plasmid, or viral vector. Details concerning how to make and use liposomal formulations can be found in, among other places, U.S. Pat. Nos. 4,016,100; 4,452,747; 4,921,706; 4,927,637; 4,944,948; 5,008,050; and 5,009,956, all of which are incorporated herein by reference.

An effective amount of any of the above-described vaccines can be determined by conventional means, starting with a low dose of virus, viral protein plasmid or viral vector, and then increasing the dosage while monitoring the effects. An effective amount may be obtained after a single administration of a vaccine or after multiple administrations of a vaccine. Known factors can be taken into consideration when determining an optimal dose per animal. These include the species, size, age and general condition of the animal, the presence of other drugs in the animal, and the like. The actual dosage is preferably chosen after consideration of the results from other animal studies (see, for example, Examples 2 and 3 below).

One method of detecting whether an adequate immune response has been achieved is to determine seroconversion and antibody titer in the animal after vaccination. The timing of vaccination and the number of boosters, if any, will preferably be determined by a doctor or veterinarian based on analysis of all relevant factors, some of which are described above.

The effective dose amount of virus, protein, infectious DNA molecule, plasmid, or viral vector, of the present invention can be determined using known techniques, taking into account factors that can be determined by one of ordinary skill in the art such as the weight of the animal to be vaccinated. The dose amount of virus of the present invention in a vaccine of the present invention preferably ranges from about 10¹ to about 10⁹ pfu (plaque forming units), more preferably from about 10² to about 10⁸ pfu, and most preferably from about 10³ to about 10⁷ pfu. The dose amount of a plasmid of the present invention in a vaccine of the present invention preferably ranges from about 0.1 mg to about 100 mg, more preferably from about 1 mg to about 10 mg, even more preferably from about 10 mg to about 1 mg. The dose amount of an infectious DNA molecule of the present invention in a vaccine of the present invention preferably ranges from about 0.1 mg to about 100 mg, more preferably from about 1 mg to about 10 mg, even more preferably from about 10 mg to about 1 mg. The dose amount of a viral vector of the present invention in a vaccine of the present invention preferably ranges from about 10¹ pfu to about 10⁹ pfu, more preferably from about 10² pfu to about 10⁸ pfu, and even more preferably from about 10³ to about 10⁷ pfu. A suitable dosage size ranges from about 0.5 ml to about 10 ml, and more preferably from about 1 ml to about 5 ml.

Suitable doses for viral protein or peptide vaccines according to the practice of the present invention range generally from 1 to 50 micrograms per dose, or higher amounts as may be determined by standard methods, with the amount of adjuvant to be determined by recognized methods in regard of each such substance. In a preferred example of the invention relating to vaccination of swine, an optimum age target for the animals is between about 1 and 21 days, which at pre-weening, may also correspond with other scheduled vaccinations such as against Mycoplasma hyopneumoniae or PCV. Additionally, a preferred schedule of vaccination for breeding sows would include similar doses, with an annual revaccination schedule.

An effective amount of any of the above-described vaccines can be determined by conventional means, starting with a low dose of virus, plasmid or viral vector, and then increasing the dosage while monitoring the effects. An effective amount may be obtained after a single administration of a vaccine or after multiple administrations of a vaccine. Known factors can be taken into consideration when determining an optimal dose per animal. These include the species, size, age and general condition of the animal, the presence of other drugs in the animal, and the like. The actual dosage is preferably chosen after consideration of the results from other animal studies.

One method of detecting whether an adequate immune response has been achieved is to determine seroconversion and antibody titer in the animal after vaccination. The timing of vaccination and the number of boosters, if any, will preferably be determined by a doctor or veterinarian based on analysis of all relevant factors, some of which are described above.

The effective dose amount of virus, infectious RNA molecule, plasmid, or viral vector, of the present invention can be determined using known techniques, taking into account factors that can be determined by one of ordinary skill in the art such as the weight of the animal to be vaccinated. By way of example, vaccines may be delivered orally, parenterally, intradermally, subcutaneously, intramuscularly, intranasally or intravenously. Oral delivery may encompass, for example, adding the compositions to the feed or drink of the animals. Factors bearing on the vaccine dosage include, for example, the weight and age of the pig.

The present invention further provides a method of preparing a vaccine comprising a PRRS virus, infectious RNA molecule, plasmid, or viral vector described herein, which method comprises combining an effective amount of one of the PRRS virus, infectious RNA molecule, plasmid, or viral vector of the present invention, with a carrier acceptable for pharmaceutical or veterinary use.

In addition the live attenuated vaccine of the present invention can be modified as described in U.S. Pat. No. 6,500,662 to encode a heterologous antigenic epitope which is inserted into the PRRS viral genome using known recombinant techniques. See also U.S. Pat. No. 7,132,106 which is incorporated by reference in its entirety. Antigenic epitopes useful as heterologous antigenic epitopes for the present invention include antigenic epitopes from a swine pathogen other than PRRS virus which include, but are not limited to, an antigenic epitope from a swine pathogen selected from the group consisting of porcine parvovirus, porcine circovirus, a porcine rotavirus, swine influenza, pseudorabies virus, transmissible gastroenteritis virus, porcine respiratory coronavirus, classical swine fever virus, African swine fever virus, encephalomyocarditis virus, porcine paramyxovirus, torque teno virus, Actinobacillus pleuropneumoniae, Actinobacillus suis, Bacillus anthraci, Bordetella bronchiseptica, Clostridium haemolyticum, Clostridium perfringens, Clostridium tetani, Escherichia coli, Erysipelothrix rhusiopathiae, Haemophilus parasuis, Leptospira spp., Mycoplasma hyopneumoniae, Mycoplasma hyorhinis, Mycoplasma hyosynovia, Pasteurella multocida, Salmonella choleraesuis, Salmonella typhimurium, Streptococcus equismilis, and Streptococcus suis. Nucleotide sequences encoding antigenic epitopes from the aforementioned swine pathogens are known in the art and can be obtained from public gene databases on the worldwide web, such as at Genbank from the (USA) National Center for Biotechnology Information.

Additional features and variations of the invention will be apparent to those skilled in the art from the entirety of this application, including the detailed description, and all such features are intended as aspects of the invention. Likewise, features of the invention described herein can be re-combined into additional embodiments that also are intended as aspects of the invention, irrespective of whether the combination of features is specifically mentioned above as an aspect or embodiment of the invention. Also, only such limitations which are described herein as critical to the invention should be viewed as such; variations of the invention lacking limitations which have not been described herein as critical are intended as aspects of the invention. It will be clear that the invention may be practiced otherwise than as particularly described in the foregoing description and examples.

Numerous modifications and variations of the present invention are possible in light of the above teachings and, therefore, are within the scope of the invention.

The following examples are intended to illustrate but not limit the invention.

EXAMPLE 1 Adaptation and Attenuation of PRRSV Isolate P129 to PK-9 Cells

Virulent PRRS isolate P129 was isolated from a sick pig in Indiana in 1995 at the Animal Disease Diagnostic Laboratory of Purdue University. A serum sample from this pig was passaged once in a high health status pig to expand serum and lung homogenate stocks. Viral RNA was extracted from the serum and lung homogenate and used to determine the complete genome consensus sequence of P129 passage 0 virus. RNA was first primed with random hexamers and used to synthesize cDNA. The genome was amplified in three overlapping pieces using high fidelity (proofreading) PCR. The PCR products from three separate PCR reactions (per genome segment) were T/A cloned and used for DNA sequencing to generate a full length genome consensus sequence (see SEQ ID NO:1).

An aliquot of the same pig serum used for DNA sequencing, containing P129 passage 0, was used to infect primary porcine alveolar macrophage (PAM) cells. The progeny virus from the PAM infection (passage 1) was filtered through a 0.1 micrometer syringe filter and used to infect PK-9 cells.

PK-9 cells are a transgenic cell line derived by stably transfecting the PK0809 porcine kidney cell line with a plasmid encoding a deleted version of the porcine CD163 gene and the neomycin resistance gene. Details of the construction and characterization of the PK-9 cell line have been described previously.

Adaptation of the passage 1 virus from PAM cells to growth on PK-9 cells was difficult, and required several attempts with multiple parallel lineages. Infection was monitored by immunofluorescence of duplicate wells using FITC-conjugated monoclonal antibody SDOW17 specific for the viral nucleocapsid protein (Rural Technologies Inc, Brookings S. Dak.). Early passages resulted in a few small foci, but did not generate enough cell-free virus particles to initiate infection of a fresh monolayer. These passages were accomplished by treating the infected monolayer with Accutase (a trypsin substitute) and reseeding the cells in multiple wells with fresh medium, with or without the addition of non-infected PK-9 cells. After several such passages, some lineages showed a clear increase in the frequency and size of fluorescent foci. Some of these had acquired the ability to be passaged using cell-free virus fluids. By passage 17 (1 on PAM cells, 16 on PK-9), one lineage could reliably be sustained using dilutions of the cell-free fluids from the previous passages, and resulted in the infection of the entire monolayer within a few days. The virus did not cause cytopathic effect on PK-9 cells at any passage level. RNA was extracted from infected PK-9 cells at virus passage 17 and used to construct an infectious cDNA clone.

EXAMPLE 2 Construction of an Infectious cDNA Clone of P129-PK Passage 17

An infectious cDNA clone of the P129-PK passage 17 virus was constructed, using a backbone plasmid as previously described. The genome of the virus was amplified by reverse transcription and PCR in three overlapping segments, with naturally occurring unique restriction endonuclease sites in the regions of overlap. The products from three separate PCR reactions were cloned and sequenced, and aligned to generate a consensus sequence for each genome segment. If none of the three cloned products of a given segment matched the predicted amino acid sequence of the consensus for that segment, one of the clones was modified by subcloning and/or site-directed mutagenesis until it matched the predicted amino acid sequence of the consensus. The three genome segments and the plasmid backbone were joined using standard cloning techniques and restriction endonuclease sites. The resulting full-length clone, designated pCMV-S-P129-PK17-FL, was infectious when transfected into PK-9 cells. The sequence of this infectious cDNA clone is given in SEQ ID NO:2. The genome is essentially identical to the passage 17 virus from which it was constructed, with authentic termini, and lacks any insertions or deletions relative to the consensus sequences of passage 17. There are no engineered restriction sites or other targeted changes within the viral genome of this infectious cDNA clone.

Nucleotide and amino acid differences between the complete genome consensus sequences of P129 passage 0 and the genome sequence of infectious clone pCMV-S-P129-PK17-FL are listed individually in Table 6. Table 6 includes all nucleotide differences and resulting amino acid differences by genome position. A subset of these mutations are responsible for the change in phenotype from IFN inhibitory (passage 0) to IFN non-inhibitory (all viruses derived from the passage 17 infectious cDNA clone). Table 7 summarizes nucleotide, amino acid, and non-conserved amino acid differences by PRRSV open reading frame (ORF) or non-structural protein (nsp). For the purposes of Table 7, the following groups of amino acids are among those considered conserved: [K, R], [D, E], [L, I, V, A], and [S, T].

EXAMPLE 3 Deletion Mutants in P129-PK Passage 17

Deletions in two areas of the genome were engineered into infectious cDNA clone pCMV-S-P129-PK17-FL, to generate five genetically modified infectious clones.

One area of the genome to undergo modification was the nuclear localization sequence (NLS) located at amino acid positions 41-47 of the nucleocapsid protein (encoded by PRRSV ORF 7). Two types of deletions were made. These deletions have been described previously within the context of another PRRSV infectious clone. The wild type sequence of amino acid residues 41-49 is PG . . . KN. In mutant “d43/44”, also known as “PG-KS”, lysine residues 43 and 44 are deleted and asparagine residue 49 is changed to a serine. In mutant “d43144146”, also known as “PG-S-KS”, lysine residues 43, 44, and 46 are deleted and asparagine residue 49 is changed to a serine. The infectious clones derived from pCMV-S-P129-PK17-FL that incorporate these deletions are pCMV-S-P129-PK17-d43/44 and pCMV-S-P129-PK17-d43/44/46 respectively. See U.S. Pat. No. 7,544,362.

The second area of the genome to undergo modification was in the hypervariable region of nsp2, within ORF1a. A deletion of 131 amino acids (393 nucleotides) has been described previously within the context of another PRRSV infectious clone. The infectious clone derived from pCMV-S-P129-PK17-FL that incorporate this deletion is pCMV-S-P129-PK17-nsp2.

Infectious clones that combine the NLS and nsp2 deletions were also generated within the pCMV-S-P129-PK17-FL backbone, and these were designated pCMV-S-P129-PK17-nsp2-d43/44 and pCMV-S-P129-PK17-nsp2-d43/44/46.

EXAMPLE 4 Generation and Growth of Viruses on PK-9 Cells

The six infectious clones described in Example 3 were transfected into PK-9 cells to generate the six viruses as shown in Table 1. Virus was generated from these infectious clones by direct transfection of the circular plasmid into PK-9 cells using Lipofectamine 2000. Following transfection, recovered viruses were again serially passaged on PK-9 cells in order to further increase titers and attenuate virulence. Stocks were made for in vitro testing and in vivo evaluation as vaccine candidates. In the case of P129-PK17-FL virus derived from the non-modified pCMV-S-P129-PK17-FL infectious clone, the virus was cultured until reaching a total of 52 passages from the pig. The complete genome of this virus was sequenced at passages 24 (SEQ ID NO: 3) and 52 (SEQ ID NO:6).

EXAMPLE 5 Viruses Derived from the P129-PK Passage 17 Infectious cDNA Clone Have Reduced Ability to Inhibit IFN-Alpha Induction

Viruses and cells. MARC-145 and ST cells were grown in modified Eagle's medium (MEM) supplemented with 5% fetal bovine serum (FBS) and antibiotics (50 μg/ml gentamicin, 100 UI penicillin and 100 μg/ml streptomycin). The porcine alveolar macrophage ZMAC-1 cells were grown in RPMI-1640 supplemented with 10% FBS. TGE virus strain Purdue was prepared by infection of confluent ST cell monolayers at a multiplicity of 0.01 in modified Eagle's medium. The virus inoculum was removed after 1 h and cells were incubated in MEM supplemented with 2.5% FBS at 37° C. in a 5% CO₂ atmosphere. Virus was released by freezing and thawing the cell monolayers after 80% cytopathic effect was observed. The TGE viral stock was centrifuged at 3,500 rpm for 15 min at 4° C. and stored at −80° C. until use. Virus stocks (from PK-9 cells) were as follows: P129-PK-FL and P129-PK-dnsp2-d43/44/46 were at passage 8/25 (8 from the infectious clone, 25 from the pig). The other four viruses (P129-PK-d43/44, P129-PK-d43/44/46, P129-PK-dnsp2, and P129-PK-dnsp2-d43/44) were at passage 21/38. Working stocks of various PRRS viruses were prepared by making a single passage on ZMAC-1 cells, except that commercial vaccines Ingelvac PRRS MLV and Ingelvac PRRS ATP were reconstituted according to the manufacturer's instructions and used directly for infection.

Isolation of porcine PBMC. Fresh heparinized venous blood was diluted with Hank's and PBMC were isolated by density centrifugation through Ficoll-Hypaque 1077 (Sigma) gradient. After being washed twice in Hank's, the cells were suspended in RPMI medium with L-glutamine (Mediatech) supplemented with 5% fetal bovine serum (Gibco), 100 U/ml penicillin, 0.1 mg/ml streptomycin, 1 mM sodium pyruvate, lx nonessential amino acids (Mediatech) 100 U/ml gentamicin and 250 mM 2-mercaptoethanol (Sigma).

Purification of porcine plasmacytoid dendritic cells. The purification of porcine plasmacytoid dendritic cells was done as previously described (Calzada-Nova, submitted), and was based on the characteristic expression of CD4 and CD172 by these cells (Summerfield et al., 2003) Briefly, fresh porcine PBMC were suspended in PBS with 0.5% BSA and labeled with optimal amounts of mAb recognizing porcine CD172 (74-22-15, VMRD). Following one wash, the cells were then incubated with secondary goat anti-mouse antibody conjugated to PE (Southern Biotech) and after washing, with FITC labeled anti-CD4 (74-12-4, VMRD). PDCs were sorted on a Reflection Cell Sorter (iCyt), sort gates were set on the CD4⁺/CD172^(low) population. After the sort the purity of the cells was confirmed by reanalysis. In all cases, the purity was >95%.

Assay for measurement cytokine secretion. PBMC or PDC were stimulated for 16 h (37° C., 5% CO₂) with the different stimulants or were mock-stimulated. After incubation, medium overlaying the stimulated cells was assayed for the presence of IFN-α using a sandwich ELISA prepared with monoclonal antibodies available commercially (anti-pig IFN-α mAbs K9 and F17). Briefly, Immulon II plates (Dynatech Inc.) were coated with anti-porcine IFN-α mAb F17 (PBL Laboratories) by overnight incubation at 4° C. followed by blocking with RPMI medium supplemented with 5% fetal bovine serum. After 1 hour the medium was discarded and fifty microliters of the supernatant to be tested added to the assay wells in duplicate. After a 1 h incubation the assay wells were washed 4 times and then incubated sequentially with biotin-labeled, anti-porcine IFN-α mAb K9 (PBL Laboratories), HRP-conjugated streptavidin (Zymed Laboratories), and TMB substrate (KPL). The optical density was determined with an ELISA plate reader.

Viruses derived from the P129-PK passage 17 infectious cDNA clone lack the ability to inhibit IFN-alpha induction. Working virus stocks were prepared from of a group of four different PRRS wild-type virus isolates (P3412, P129, IND5, NADC20) utilizing the porcine alveolar macrophage cell line ZMAC-1. Additional stocks were also prepared from derivatives of the first two wild-type viruses which had been adapted to grow in cell culture by repeated passage in PK-9, FK.D4 or MARC-145 cells. Three of the four wild-type isolates (P129, IND5, NADC20) grew readily and efficiently in the ZMAC-1 cells to titers of about 10⁷ TCID₅₀/ml, while the P3412 wild-type isolate reached a titer of only 10⁵ TCID₅₀/ml. Notably, stocks of P129 viruses prepared in the ZMAC-1 cell line reached 10-fold higher titers than those obtained in the PK-9 or MARC-145 cells to which the viruses were adapted. Examination of the ability of these viruses to stimulate IFN-α secretion by PBMC revealed that with one exception (isolate P3412 clone C), a very small amount (<50 pg) of IFN-α was secreted by these cells in response to their exposure to any of the PRRS virus stocks tested, which is negligible by comparison to the abundant secretion of IFN-α (17,540 pg) produced by the same cells as a result of their exposure to the porcine coronavirus, transmissible gastroenteritis virus (TGEv).

PRRSV is not only unable to stimulate IFN-α production by porcine PBMC but actively inhibits its production. The inhibitory effects of the PRRSV stocks were determined by measuring the amount of IFN-α secreted by PBMC in response to exposure to TGEv in the presence or absence of PRRSV. As shown in Table 2, all 4 of the wild-type PRRS virus isolates tested, as well as all of the cell culture adapted derivatives, exhibited a strong inhibitory effect (>80%) on the IFN-α response of PBMC to TGEv. The analysis of a group of virus stocks derived from an infectious cDNA clone (pCMV-S-P129-PK17-FL), including full-length P129-PK-FL virus and several genetically engineered deletion mutants was conducted. As shown in Table 3, when compared to the strong inhibitory effect (95%) of the parental wild-type isolate P129 (passage 1), the P129-PK-FL virus and all deletion mutants exhibited a significantly reduced ability to inhibit the induction of IFN-□ by TGEv in PBMC. To further evaluate the IFN-α phenotype of these viruses, subsequent experiments were focused on performing direct comparisons between the P129-PK-FL and P129-PK-d43/44 viruses, the parental P129 wild-type strain, and/or two commercially available modified live PRRSV vaccines produced by Boehringer Ingelheim (Ingelvac PRRS MLV and Ingelvac PRRS ATP). An additional low-passage reference isolate, NVSL-14, was also tested. As shown in Table 4, in four independent experiments, P129-PK-FL and P129-PK-d43/44 exhibited significantly lesser IFN-α inhibitory effect than the parental P129 virus, the two Ingelvac attenuated strains, or the reference strain. In one instance, co-infection with the P129-PK-FL or P129-PK-d43/44 viruses resulted in an apparent enhancement of the IFN-α response to TGEv.

The results shown in Table 2 are indicative of the interferon-α inhibitory effect of wild-type PRRS virus and derivatives adapted to growth in cell culture. The indicated PRRS virus stocks, were grown in ZMAC-1 cells and the titer of these newly generated stocks determined using ZMAC-1 cells. The amount of IFN-α present in culture supernatants of porcine peripheral blood mononuclear cells exposed for 18 h to the indicated PRRS virus stock in the presence or absence of TGE virus was determined by ELISA. *Response to TGEv alone.

The results shown in Table 3 demonstrate the interferon-α inhibitory effect of wild-type PRRS virus P129 and its genetically engineered derivatives adapted to grow in CD163-expressing PK-9 cells. The amount of IFN-α present in culture supernatants of porcine peripheral blood mononuclear cells (PBMC) exposed for 18 h to the indicated PRRS virus stock in the presence or absence of TGE virus was determined by ELISA. na=not applicable; *Response to TGEv alone.

Table 4 shows decreased interferon-α inhibitory effect of the P129-PK-FL and P129-PK-d43/44 viruses as compared to the wild-type P129 virus and the PRRS Ingelvac vaccines. The amount of IFN-α present in culture supernatants of porcine peripheral blood mononuclear cells (PBMC) exposed for 18 h to the indicated PRRS virus stock in the presence or absence of TGE virus was determined by ELISA. na=not applicable; *Response to TGEV alone.

The plentiful amount of IFN-α secreted by PBMC in response to their exposure to TGEV is derived primarily from a subset of cells that comprise less than 0.3% of the PBMC population. This infrequent but important cell subset is composed of plasmacytoid dendritic cells (PDCs), which received this name due to characteristic plasmacytoid morphology. To further examine the IFN-α phenotype of the P129-PK-FL and the P129-PK-d43/44 viruses, a series of experiments was performed similar to those described above, except that PDC freshly isolated from PBMC to a >95% purity were utilized. As shown in FIG. 1, this series of experiments confirmed that the P129-PK-FL and P129-PK-d43/44 viruses caused negligible inhibition of IFN-α induction by TGEV. Furthermore, in one experiment an apparent enhancing effect was observed on TGEV-mediated IFN-α induction by PDCs in response to P129-PK-FL and P129-PK-d43/44 PRRS viruses. In contrast, the Ingelvac PRRS MLV virus exhibited a strong inhibitory effect on the IFN-α response, as shown in FIG. 1.

The results described in the experimental section reveal that the P129-PK-FL and P129-PK-d43/44 PRRS viruses, as well as other derivatives of the pCMV-S-P129-PK17-FL infectious cDNA clone, have a greatly reduced ability to inhibit the induction of IFN-α by TGEV in infected PBMC or PDC cells. This is in marked contrast to the IFN suppressive effect observed with wild-type (low-passage) PRRS viruses and with two commercially available modified live virus vaccines (Ingelvac PRRS MLV and Ingelvac PRRS ATP). The observation that the P129-PK-FL and P129-PK-d43/44 viruses were minimally suppressive of this important function of PDCs is potentially significant given the major role that these cells play in mediating innate immunity against virus infections.

It should also be noted that the present invention provides clinically effective commercial vaccine viruses adapted to grow on permissive cells that recombinantly express CD163 receptor, and that such viruses and vaccines are not dependent on, nor were developed at any point with, historical “simian cell” culturing technology. See specifically U.S. Pat. No. 7,754,464.

EXAMPLE 6 Safety and Efficacy of Vaccine Candidates

In order to evaluate their safety and efficacy as vaccines against PRRS, three of the viruses derived from the pCMV-S-P129-PK17-FL infectious cDNA clone, P129-PK-FL (passage 7/24), P129-PK-d43/44 (passage 17/34) and P129-PK-d43/44/46 (passage 17/34) were evaluated in a young pig respiratory disease model. The origin of these viruses is shown in FIG. 8, and the experimental design (treatment groups) are listed in Table 5. Low passage virulent PRRSV isolate NADC20 was used for heterologous challenge at 7 weeks of age (four week past vaccination). Control treatment groups included mock vaccine and commercial PRRS vaccine Ingelvac MLV.

Non-treated (NT) groups were as follows: NT1 pigs were sentinels to monitor the health status of source pigs. They were housed separately and were necropsied prior to PRRSV challenge. NT2 pigs were contact controls housed separately in a pen between the two pens of vaccinated pigs, a total of two per treatment group for each T02 thru T05. NT3 pigs were contact controls housed one per pen with vaccinated pigs, a total of two per treatment group (T01 thru T05). Only NT3 pigs were assigned to the T01 group.

Rectal temperatures of vaccinated animals were measured post-vaccination and compared to the T01 (mock vaccine) treatment group. The results are shown in FIG. 1. None of the vaccines induced fevers. All groups averaged less than 104° C. throughout the post-vaccination observation period.

Rectal temperatures of pigs were measured post-challenge. The results are shown in FIG. 2. Unvaccinated T01 pigs showed sustained fevers of greater than 104° C. In contrast, three of the vaccines significantly reduced post-challenge fevers. P129-PK-FL was most effective at reducing fevers.

The body weight of animals was recorded pre- and post-vaccination. The results are shown in FIG. 3. Body weights were recorded on days −1 (prior to vaccination), 10, 24, 27 (prior to challenge), and 37 of the study. In unvaccinated pigs, challenge with virulent NADC20 virus almost completely eliminated weight gain during the 10 day observation period. The vaccines negated this effect to various degrees.

The lungs of challenged animals were examined at necropsied post-challenge. The percentages of each lung involved in lesions are shown in FIG. 4. The T01 mock vaccine group averaged 25.1% lung lesion involvement. The vaccines reduced lung lesions to various degrees. P129-PK-FL was most efficacious, reducing lung lesion involvement to 1.1%.

The severity of the lung lesions was evaluated using a lung assessment score (LAS) as shown in FIG. 5. Three of the vaccines reduced LAS. P129-PK-FL reduced the mean LAS from 1.63 in the mock vaccinated group to 0.14.

Serum antibodies to PRRSV were induced by both vaccination and challenge. The IDEXX ELISA S/P ratios were measured on days 27 and 37 of the study. The results are shown in FIG. 6. Vaccination with P129-PK-FL induced the highest levels of anti-PRRS antibodies.

Viremia in the serum of challenged pigs was titrated on PAM cells. Results (TCID₅₀/mL) are given in FIG. 7. P129-PK-FL was most effective at reducing post-challenge viremia.

Although the invention has been described with reference to the above examples, and to Attachments, the entire content of each of which are incorporated by reference in their entireties, it will be understood that modifications and variations are encompassed within the spirit and scope of the invention. Accordingly, the invention is limited only by the following claims.

EXAMPLE 7 Derivation of Infectious cDNA Clone PCMV-S-P129-PK17-FL from Infectious cDNA Clone PCMV-S-P129

The PRRSV infectious cDNA clone of the present invention pCMV-S-P129-PK17-FL can readily be derived from the previously described PRRSV infectious cDNA clone pCMV-S-P129 by one of ordinary skill in the art, using the technique of site-directed mutagenesis. PRRSV infectious cDNA clone pCMV-S-P129 is described in U.S. Pat. No. 6,500,662 and deposited with ATCC under accession number 203489. The DNA sequence of the PRRSV genome in this clone also available in the Genbank (NCBI) database as accession number AF494042. Site-directed mutagenesis kits are commercially available from a number of suppliers, and are capable of making numerous simultaneous nucleotide changes at multiple sites in large plasmids. Such kits include, but are not limited to, Change-IT™ Multiple Mutation Site Directed Mutagenesis Kit (Affymetrix/USB), QuikChange Lightning Multi Site-Directed Mutagenesis Kit (Agilent Technologies—Stratagene Products), and AMAP Multi Site-directed Mutagenesis Kit (MBL International).

A list of nucleotide changes between PRRSV infectious cDNA clone pCMV-S-P129 (available from ATCC) and the PRRSV infectious cDNA clone of the present invention pCMV-S-P129-PK17-FL is presented in Table 8. All changes are in the protein coding regions of the genome. There are a total of 74 nucleotide changes, which can be introduced into the pCMV-S-P129 infectious clone using 74 mutagenic primers and multiple sequential reactions with a commercial site-directed mutagenesis kit, yielding a plasmid molecule that is identical in sequence to pCMV-S-P129-PK17-FL described herein. In actuality, one can get the same result with fewer than 74 mutagenic primers, since clusters of mutations within about 50-60 nucleotides of each other can be changed using a single mutagenic primer. For example, nucleotides 735, 750, and 756 can be changed using a single mutagenic primer, as can nucleotides 965, 992, and 1009. Thus the number of primers is reduced to about 60.

Of the 74 nucleotide changes, the majority (42) are synonymous or “silent”, meaning they encode the same amino acid. These nucleotide changes are unlikely to have any measurable effect on the interferon induction or inhibition phenotype of the virus. The remaining 32 nucleotide changes are non-synonymous or “non-silent”, and result in amino acid changes in viral proteins. These 32 nucleotide changes are predicted to be directly responsible for the interferon induction/inhibition phenotype of the virus, and should be changed in order to convert the virus encoded by the infectious clone pCMV-S-P129 to the same interferon phenotype as the shown by the virus encoded by infectious clone pCMV-S-P129-PK17-FL. Such a change would require at most 32 mutagenic primers, less if one takes into account the clustering of some of the relevant nucleotides.

EXAMPLE 8 De Novo Synthesis of Infectious cDNA Clone PCMV-S-P129-PK17-FL

As an alternative to site-directed mutagenesis, the PRRS viral genome of the present invention can be chemically synthesized de novo, with appropriate 5′ and 3′ adaptor sequences, and cloned into the plasmid backbone used for PRRS infectious cDNA clone pCMV-S-P129 (available from ATCC as accession number 203489) or a similar plasmid backbone. Custom synthesis of genes greater than 50 kb in length (the PRRSV genome is about 15.5 kb) is available as a commercial service from numerous vendors, including (but not limited to): GenScript, DNA 2.0, and Bio Basic Inc. The synthetic viral genome is directionally cloned into the pCMV-S vector by replacing the viral genome in the infectious clone pCMV-S-P129 using the 5′ PacI and 3′ SpeI restriction enzyme sites that flank the genome. In order to cut the synthetic genome, a 24-nucleotide extension

(5′-GCAGAGCTCGTTAATTAAACCGTC-genome-3′, which includes the underlined PacI site) is built into the 5′ end of the synthetic genome, and an 83-nucleotide extension (5′-genome-AAAAAAAAAAAAAAAAAAAAATGCATATTTAAATCCCAAGCCGAATTCCAGCACA CTGGCGGCCGTTACTAGTGAGCGGCCGC-3′, which includes the underlined SpeI site) is built into the 3′ end of the synthetic genome. After cutting the plasmid and synthetic genome with PacI and SpeI, the appropriate fragments are purified, joined using DNA ligase, and transformed into Escherichia coli for screening and propagation using standard cloning techniques well known to persons of ordinary skill in the art.

Deposit of Biological Materials

The following biological materials (see U.S. Pat. No. 6,500,662) were deposited with the American Type Culture Collection (ATCC) at 10801 University Blvd., Manassas, Va., 20110-2209, USA on Nov. 19, 1998, and were assigned the following accession numbers.

Plasmid pT7P129A, accession number 203488

Plasmid pCMV-S-P129, accession number 203489

The complete text and disclosure of the following United States Patents is incorporated herein by reference, as if fully set forth: U.S. Pat. Nos. 6,500,662, and 7,618,797.

TABLE 1 Infectious clone Virus pCMV-S-P129-PK17-FL P129-PK-FL pCMV-S-P129-PK17-d43/44 P129-PK-d43/44 pCMV-S-P129-PK17-d43/44/46 P129-PK-d43/44/46 pCMV-S-P129-PK17-nsp2 P129-PK-nsp2 pCMV-S-P129-PK17-nsp2-d43/44/46 P129-PK-nsp2-d43/44 pCMV-S-P129-PK17-nsp2-d43/44/46 P129-PK-nsp2-d43/44/46

TABLE 2 PRRS virus IFN-α Esti- titer IFN-α (ng/ml) mated (TCID₅₀) (ng/ml) produced PRRS in PRRS produced by virus virus by PBMC PBMC titer stocks in in Inhibition (TCID₅₀) generated response response of IFN-α Passage/ in in to to response PRRSv Cell original ZMAC-1 PRRSv PRSSv + to TGEv SAMPLE stock CLONE type stock cells alone TGEv (%) 1 P3412 wt 0 (serum) nd 10⁵ <0.04 <0.04 99 2 P3412 A 41/PK 10³ 10³ <0.04 1.166 93 3 P3412 C 41/PK 10³ 10³ 0.464 3.376 81 4 P3412 A 43/FK 10⁵ 10⁶ <0.04 <0.04 99 5 P3412 B 43/FK 10⁵ 10⁵ <0.04 1.86 89 6 P129 wt 0 (serum) nd 10⁷ <0.04 0.327 98 7 P129 A 63/PK 10⁴ 10⁸ <0.04 <0.04 99 8 P129 B 63/PK 10⁴ 10⁸ <0.04 2.3 87 9 P129 A 60/FK 10⁵ 10⁶ 0.05 2.151 88 10 P129 B 60/FK 10⁵ 10⁶ <0.04 <0.04 99 11 P129 A-1   51/MARC 10⁵ 10⁸ <0.04 0.686 96 12 P129 A-1   151/MARC 10⁵ 10⁸ <0.04 0.04 99 13 NADC wt 0 (serum) nd 10⁷ <0.04 <0.04 99 20 14 IND5 wt 0 (serum) nd 10⁷ <0.04 <0.04 99 — Mock — — na na 0 17.54* na

TABLE 3 IFN-α IFN-□α (ng/ml) (ng/ml) Inhibition produced produced of TGEv by PBMC by PBMC induced in response in response IFN-α Exper- to PRRSv to PRRSv + response iment PRRS virus stock alone TGEv (%) 1 P129 0.09 0.64 95 P129-PK-FL 0.53 7.37 38 P129-PK-d43/44 0.85 8.59 28 P129-PK-d43/44/46 1.01 7.65 36 P129-PK- 1.34 10.28 24 dnsp2d43/44 P129-PK- 0.38 8.28 31 dnsp2d43/44/46 P129-PK-dnsp2 0.04 4.86 60 Mock na 12.16* na

TABLE 4 IFN-α IFN-□α (ng/ml) (ng/ml) Inhibition produced produced of TGEv by PBMC by PBMC induced in response in response IFN-α Exper- to PRRSv to PRRSv + response iment PRRS virus stock alone TGEv (%) 1 P129 0.04 9.75 81 P129-PK-FL 0.07 60.22 0 P129-PK-d43/44 0.13 70.10 0 Ingelvac PRRS 0.04 13.05 74 Ingelvac PRRS 0.04 9.10 82 ATP NVSL-14 0.01 13.35 74 Mock na 50.06* na 2 P129-PK-FL 0.126 13.52 26 P129-PK-d43/44 0.127 17.18 6 Ingelvac PRRS 0.04 3.09 83 Ingelvac PRRS 0.04 3.11 83 ATP Mock na 18.21* na 3 P129-PK-FL 0.04 8.28 6 P129-PK-d43/44 0.06 8.26 6 Ingelvac PRRS 0.04 3.56 60 Ingelvac PRRS 0.04 4.15 53 ATP Mock na 8.84* na 4 P129-PK-FL 0.05 12.97 7 P129-PK-d43/44 0.05 13.57 3 Ingelvac PRRS 0.04 6.07 57 Ingelvac PRRS 0.04 5.30 62 ATP Mock na 13.95* na

TABLE 5 Passage Volume or Cell per IM # of TX IVP Serial # Line Regimen Dose Pigs NT1* NA NA NA NA NA 3 NT2* NA NA NA NA NA 8 NT3* NA NA NA NA NA 10 T01 Mock NA NA Day 0 2 mL 12 T02 P129-PK-d43/44 17/34 PK9 Day 0 2 mL 12 T03 P129-PK-d43/44/46 17/34 PK9 Day 0 2 mL 12 T04 P129-PK-FL  7/24 PK9 Day 0 2 mL 12 T05 BI (Ingelvac NA Monkey Day 0 2 mL 12 MLV) kidney

TABLE 6 Passage Passage Passage Passage Affected Amino 0 17 Genome 0 17 viral acid amino amino position nucleotide nucleotide protein position acid acid 407 C T Nsp1a 72 P P 612 C T Nsp1a 141 H Y 735 G A Nsp1b 2 D N 750 A G Nsp1b 7 S G 756 G A Nsp1b 9 D N 992 A T Nsp1b 87 E D 1009 G A Nsp1b 93 C Y 1096 C A Nsp1b 122 P H 1215 C T Nsp1b 162 L L 1620 G A Nsp2 94 A T 1786 C A Nsp2 149 T K 1793 C T Nsp2 151 G G 1808 T C Nsp2 156 D D 1841 C T Nsp2 167 C C 2106 A G Nsp2 256 I V 2164 T G Nsp2 275 M R 2185 T C Nsp2 282 M T 2318 A G Nsp2 326 S S 2403 G T Nsp2 355 V L 2591 G A Nsp2 417 L L 2804 C T Nsp2 488 D D 3019 A G Nsp2 560 Y C 3074 T C Nsp2 578 S S 3167 C T Nsp2 609 D D 3214 G A Nsp2 625 R K 3563 C T Nsp2 741 I I 3740 A G Nsp2 800 A A 4154 T C Nsp2 938 C C 4477 A C Nsp3 72 K T 4643 A G Nsp3 127 V V 4705 T C Nsp3 148 V A 4736 C T Nsp3 158 P P 5231 C T Nsp3 323 I I 5324 C T Nsp3 354 L L 5393 G A Nsp3 377 L L 5498 A G Nsp3 412 L L 5851 C A Nsp4 84 A E 5855 T C Nsp4 85 D D 5909 C T Nsp4 103 V V 5917 G A Nsp4 106 S N 5985 C A Nsp4 129 L I 6505 C T Nsp5 98 A V 6644 T C Nsp5 144 F F 6653 T C Nsp5 147 R R 7419 G A Nsp7 217 D N 8032 A G Nsp9 162 A A 8074 C T Nsp9 176 G G 8200 A G Nsp9 218 G G 8593 T C Nsp9 349 P P 8831 G A Nsp9 429 V I 8911 T C Nsp9 455 N N 9160 A G Nsp9 538 E E 9568 A G Nsp9 674 L L 9714 T C Nsp10 38 I T 10,271 C T Nsp10 224 L L 10,627 T C Nsp10 342 V V 11,265 G A Nsp11 114 G E 11,512 T C Nsp11 196 S S 11,913 T C Nsp12 107 I T 12,487 A T ORF2a 144 E V 12,876 C T ORF3 66 A V 12,949 A G ORF3 90 L L 13,575 G A ORF4 117 V V 13,857 T G ORF5 29 V G 13,869 A G ORF5 33 N S 13,872 C G ORF5 34 T S 14,102 G A ORF5 111 V I 14,143 C T ORF5 124 V V 14,257 G A ORF5 162 E E 14,287 C T ORF5 172 N N 14,379 T C ORF6 7 D D 14,546 T C ORF6 63 V A 14,578 A G ORF6 74 T A 14,780 C T ORF6 141 T I 14,932 T C ORF7 20 N N 14,973 G A ORF7 34 S N 15,124 T C ORF7 84 N N 15,288 G A 3' UTR — — —

TABLE 7 Non-conservative Nucleotide Amino acid amino acid ORF or nsp differences differences differences Nsp1a 2 1 1 Nsp1b 7 6 5 Nsp2 19 8 5 Nsp3 8 2 1 Nsp4 5 3 2 Nsp5 3 1 0 Nsp6 0 0 0 Nsp7 1 1 1 Nsp8 0 0 0 Nsp9 8 1 0 Nsp10 3 1 1 Nsp11 2 1 1 Nsp12 1 1 1 ORF2a 1 1 1 ORF2b 0 0 0 ORF3 2 1 0 ORF4 1 0 0 ORF5 7 4 2 ORF6 4 3 2 ORF7 3 1 1

TABLE 8 Passage 10 (on Passage Passage Passage MARC- 17 (on 10 on 17 on 145 PK-9 MARC- PK-9 Affected Amino cells) cells) Genome 145 cells cells viral acid amino amino position nucleotide nucleotide protein position acid acid 407 C T Nsp1a 72 P P 612 C T Nsp1a 141 H Y 735 G A Nsp1b 2 D N 750 A G Nsp1b 7 S G 756 G A Nsp1b 9 D N 965 T C Nsp1b 78 G G 992 A T Nsp1b 87 E D 1009 G A Nsp1b 93 C Y 1096 C A Nsp1b 122 P H 1215 C T Nsp1b 162 L L 1376 A G Nsp2 12 A A 1395 T C Nsp2 19 C R 1871 A G Nsp2 177 L L 2185 T C Nsp2 282 M T 2235 G A Nsp2 299 D N 2403 G T Nsp2 355 V L 2731 A G Nsp2 464 Y C 2804 C T Nsp2 488 D D 2918 T C Nsp2 526 S S 3019 A G Nsp2 560 Y C 3067 G A Nsp2 576 G E 3074 T C Nsp2 578 S S 3214 G A Nsp2 625 R K 3256 T C Nsp2 639 L S 3563 C T Nsp2 741 I I 3740 A G Nsp2 800 A A 4154 T C Nsp2 938 C C 4477 A C Nsp3 72 K T 4643 A G Nsp3 127 V V 4705 T C Nsp3 148 V A 4736 C T Nsp3 158 P P 4784 C T Nsp3 174 V V 5231 C T Nsp3 323 I I 5324 C T Nsp3 354 L L 5498 A G Nsp3 412 L L 5855 T C Nsp4 85 D D 5862 G A Nsp4 88 A T 5985 C A Nsp4 129 L I 6155 T C Nsp4 185 D D 6505 C T Nsp5 98 A V 6776 A G Nsp7 2 L L 7419 G A Nsp7 217 D N 7521 T C Nsp7 251 S P 8032 A G Nsp9 162 A A 8074 C T Nsp9 176 G G 8200 A G Nsp9 218 G G 8263 T C Nsp9 239 S S 8485 T C Nsp9 313 H H 8593 T C Nsp9 349 P P 8831 G A Nsp9 429 V I 8911 T C Nsp9 455 N N 9022 A G Nsp9 492 L L 9714 T C Nsp10 38 I T 9934 C T Nsp10 111 N N 10,237 G A Nsp10 212 L L 10,271 C T Nsp10 224 L L 10,333 T C Nsp10 244 L L 10,520 A G Nsp10 307 M V 10,627 T C Nsp10 342 V V 10,847 A C Nsp10 416 I L 10,867 C T Nsp10 422 F F 10,936 C T Nsp11 4 S S 11,512 T C Nsp11 196 S S 12,949 A G ORF3 90 L L 13,452 C T ORF4 76 P P 13,575 G A ORF4 117 V V 13,843 T G ORF5 24 C W 13,860 G A ORF5 30 S N 14,287 C T ORF5 172 N N 14,481 A G ORF6 41 L L 14,546 T C ORF6 63 V A 14,578 A G ORF6 74 T A 14,780 C T ORF6 141 T I 14,932 T C ORF7 20 N N

TABLE 9 Amino acid changes responsible for reduced interferon inhibition and attenuation of virulence. Nsp and Passage Genome ORF and position position Passage 0 17 amino Passage 52 Position (nt) (aa) (aa) amino acid acid amino acid 735 ORF1a: 182 Nsp1b: 2 AMADVYD AMANVYD AMANVYD 756 ORF1a: 189 Nsp1b: 9 ISHDAVM IGHNAVM IGHNAVM 992 ORF1a: 267 Nsp1b: 87 TVPEGNC TVPDGNC TVPDGNC 1009 ORF1a: 273 Nsp1b: 93 CWWCLFD CWWYLFD CWWYLFD 1096 ORF1a: 302 Nsp1b: HGVPGKY HGVHGKY HGVHGKY 122 2106 ORF1a: 639 Nsp2: 256 AAKIDQY AAKVDQY AAKVDQY 2185 ORF1a: 665 Nsp2: 282 PSAMDTS PSATDTS PSATDTS 2403 ORF1a: 738 Nsp2: 355 LVSVLSK LNSLLSK LNSLLSK 3019 ORF1a: 943 Nsp2: 560 APMYQDE APMCQDE APMCQDE 4477 ORF1a: 1429 Nsp3: 72 CAPKGMD CAPTGMD CAPTGMD 4705 ORF1a: 1505 Nsp3: 148 PKVVKVS PKVAKVS PKVAKVS 5985 ORF1a: 1932 Nsp4: 129 AGELVGV AGEIVGV AGEIVGV 7419 ORF1a: 2410 Nsp7: 217 ADFDPEK ADFNPEK ADFNPEK 8831 ORF1a/1b: 2881 Nsp9: 429 QTPVLGR QTPILGR QTPILGR 13,857 ORF5: 29 — AVLVNAN AVLGNAN AVLGNAN 14,578 ORF6: 74 — VALTMGA VALAMGA VALAMGA 14,780 ORF6: 141 — PGSTTVN PGSITVN PGSITVN

TABLE 10 Amino acid changes responsible for reduced interferon inhibition and attenuation of virulence Nsp and Passage Genome ORF and position Passage 0 17 amino Passage 52 Position (nt) position (aa) (aa) amino acid acid amino acid 735 ORF1a: 182 Nsp1b: 2 AMADVYD AMANVYD AMANVYD 756 ORF1a: 189 Nsp1b: 9 ISHDAVM IGHNAVM IGHNAVM 1009 ORF1a: 273 Nsp1b: 93 CWWCLFD CWWYLFD CWWYLFD 1096 ORF1a: 302 Nsp1b: HGVPGKY HGVHGKY HGVHGKY 122 2185 ORF1a: 665 Nsp2: 282 PSAMDTS PSATDTS PSATDTS 3019 ORF1a: 943 Nsp2: 560 APMYQDE APMCQDE APMCQDE 4477 ORF1a: 1429 Nsp3: 72 CAPKGMD CAPTGMD CAPTGMD 4705 ORF1a: 1505 Nsp3: 148 PKVVKVS PKVAKVS PKVAKVS 7419 ORF1a: 2410 Nsp7: 217 ADFDPEK ADFNPEK ADFNPEK 

The invention claimed is:
 1. An isolated Porcine Reproductive and Respiratory Syndrome Virus (PRRS) wherein the protein thereof encoded by ORF1a is selected from a group consisting of those amino acid sequences that contain: a) one, two, three or four of: an amino acid N within the amino acid sequence AMANVYD (SEQ ID NO: 9); an amino acid N within the amino acid sequence IGHNAVM (SEQ ID NO: 12); an amino acid Y within the amino acid sequence CWWYLFD (SEQ ID NO: 18); and an amino acid H within the amino acid sequence HGVHGKY (SEQ ID NO: 21); and b) one or both of: an amino acid T within the amino acid sequence PSATDTS (SEQ ID NO: 27); and an amino acid C within the amino acid sequence APMCQDE (SEQ ID NO: 33); and c) one or both of: an amino acid T within the amino acid sequence CAPTGMD (SEQ ID NO: 36); and an amino acid A within the amino acid sequence PKVAKVS (SEQ ID NO: 39); and d) an amino acid N within the amino acid sequence ADFNPEK (SEQ ID NO: 45).
 2. A plasmid capable of directly transfecting a suitable host cell and expressing a Porcine Reproductive and Respiratory Syndrome Virus (PRRS) from the suitable host cell so transfected, which plasmid comprises: (a) a DNA sequence encoding an infectious RNA molecule encoding the PRRS virus, and (b) a promoter capable of transcribing said infectious RNA molecule, wherein the protein encoded by ORF1a of said virus has an amino acid sequence that contains: (1) one, two, three, or four of an amino acid N within the amino acid sequence ANV (see SEQ ID NO: 9); an amino acid N within the amino acid sequence HNA (see SEQ ID NO: 12); an amino acid Y within the amino acid sequence WYL (see SEQ ID NO: 18); and an amino acid H within the amino acid sequence VHG (see SEQ ID NO: 21), and (2) one or both of an amino acid T within the amino acid sequence ATD (see SEQ ID NO: 27); and an amino acid C within the amino acid sequence MCQ (see SEQ ID NO: 33) and (3) one or both of an amino acid T within the amino acid sequence PTG (see SEQ ID NO: 36); and an amino acid A within the amino acid sequence VAK (see SEQ ID NO: 39); and (4) an amino acid N within the amino acid sequence FNP (see SEQ ID NO: 45).
 3. The plasmid of claim 2, wherein the promoter is a eukaryotic promoter capable of permitting a DNA launch in targeted eukaryotic cells.
 4. The plasmid of claim 2, wherein the promoter is a prokaryotic or phage promoter capable of directing in vitro transcription of the plasmid.
 5. A method of generating a PRRS virus, which method comprises transfecting a suitable host cell with a plasmid according to claim 3, and obtaining PRRS virus generated by the transfected cell.
 6. A method of generating a PRRS virus, which method comprises transcribing the plasmid of claim
 4. 7. An isolated polynucleotide molecule comprising a DNA sequence encoding an infectious RNA molecule encoding a North American PRRS virus, wherein said DNA sequence is selected from the group consisting of: (a) a sequence that has at least 85% identity to SEQ ID NO:6, wherein the protein encoded by ORF1a thereof has an amino acid sequence that contains: (1) one, two, three, or four of: an amino acid N within the amino acid sequence ANV (see SEQ ID NO: 9); an amino acid N within the amino acid sequence HNA (see SEQ ID NO: 12); an amino acid Y within the amino acid sequence WYL (see SEQ ID NO: 18); and an amino acid H within the amino acid sequence VHG (see SEQ ID NO: 21) and (2) one or both of an amino acid T within the amino acid sequence ATD (see SEQ ID NO: 27); and an amino acid C within the amino acid sequence MCQ (see SEQ ID NO: 33), or any subset thereof; and (3) one or both of an amino acid T within the amino acid sequence PTG (see SEQ ID NO: 36); and an amino acid A within the amino acid sequence VAK (see SEQ ID NO: 39), and (4) an amino acid N within the amino acid sequence FNP (see SEQ ID NO: 45); and (b) a DNA sequence that hybridizes to the complement of a DNA sequence of (b) under highly stringent conditions which comprise hybridization to filter bound DNA in 0.5 M NaHPo4, 7% SDS, 1 mM EDTA at 65 degrees C., and washing in 0.1 SSC/0/1% SDS at 68 degrees C.
 8. A vaccine for protecting a porcine animal against infection by a PRRS virus, which vaccine comprises (a) a genetically modified North American PRRS virus encoded by the polynucleotide molecule according to claim 7, (b) said infectious molecule, (c) said polynucleotide molecule in the form of a plasmid, or (d) a viral vector comprising said polynucleotide molecule, wherein the PRRS virus is able to elicit an effective immunoprotective response against infection by PRRS virus, in an amount effective to produce immunoprotection against infection, and a carrier suitable for veterinary use. 